22
\$\begingroup\$

Write a GOLF assembly program that reads an integer from stdin (followed by a trailing newline), and outputs its prime factors seperated by newlines, followed by a trailing newline on stdout.

The prime factors need not be in a particular order. 1 is not a prime factor.

Your GOLF binary (after assembling) must fit in 8192 bytes.


Your program will be scored by running it 10 times, each with one of the following inputs:

8831269065180497  
2843901546547359024
6111061272747645669 
11554045868611683619 
6764921230558061729 
16870180535862877896 
3778974635503891117 
204667546124958269 
16927447722109721827 
9929766466606501253 

These numbers are roughly sorted in terms of difficulty. The first one should easily be solvable by trial division.

Optimization towards this set of numbers is against the spirit of the question, I may change the set of numbers at any point. Your program must work for any positive 64-bit input number, not just these.

Your score is the sum of CPU cycles used to factor the above numbers.


Because GOLF is very new I'll include some pointers here. You should read the GOLF specification with all instructions and cycle costs. In the Github repository example programs can be found. In particular look at the factorial example program, which demonstrates input/output.

Compile your program to a binary by running python3 assemble.py your_source.golf. Then run your program using python3 golf.py your_source.bin, this should print the cycle count as well. See the values of the register contents at program exit with the -d flag - use --help to see all flags.

\$\endgroup\$
8
  • 1
    \$\begingroup\$ About golf: what do you mean by "Signed division and modulus work like they do in Python - the sign of the result is the same as the sign of the divisor"? -4/-2 should be -2? (I don't think so) \$\endgroup\$
    – edc65
    Apr 25 '15 at 16:50
  • 1
    \$\begingroup\$ @edc65 Sorry, the sign portion only applies to modulus, I'll edit the docs. \$\endgroup\$
    – orlp
    Apr 25 '15 at 16:51
  • \$\begingroup\$ Just a friendly reminder that comments are not meant for extended discussion. I've migrated the comments to chat and cleaned them up here. \$\endgroup\$ Apr 25 '15 at 18:00
  • \$\begingroup\$ If the program must work for any 64-bit input integer, what happens if the input is prime? Since 1 is not a prime factor, should it only print the input integer? \$\endgroup\$
    – mbomb007
    Apr 27 '15 at 20:45
  • \$\begingroup\$ @mbomb007 Correct, it should only print the input integer. \$\endgroup\$
    – orlp
    Apr 27 '15 at 20:54
7
\$\begingroup\$

Total 36,757,269,913 cycles

830B assembled

Number                Time (s)  Cycles
    8831269065180497       0.1         1148
 2843901546547359024      55.0      9535194
 6111061272747645669     351.4     60559378
11554045868611683619       0.8       135135
 6764921230558061729       1.0       155407
16870180535862877896   43067.5   7126449414
 3778974635503891117     148.7     22823483
  204667546124958269      87.4     13635943
16927447722109721827   16119.0   2739172134
 9929766466606501253  156158.3  26784802677

Factorization by trial division, with a few optimizations. Probably not the fastest, but as no one else has posted yet, I'll kick it off.

main:
    call read
    call factor
    halt 0


# Prints factors. Pass number to be factored in register `a'.
factor:
    mov n, a # Write routine expects factor in `a', so we'll just keep it there.
    # Handle 2 specially
_factor_twos:               # do {
    geu b, n, 1
    jz _factor_ret, b   #   if (number <= 1) return
    and b, n, 1
    jnz _factor_rest, b #   if (number & 1 != 0) break
    mov a, 2
    call write          #   printf("%llu\n", 2)
    shr n, n, 1         #   number >>= 1
    jmp _factor_twos    # } while (0)
_factor_rest:
    mov a, 3            # factor = 3
_factor_rest_loop:          # do {
    cmp b, n, 1 
    jnz _factor_ret, b  #   if (number == 1) return
    divu b, c, n, a     #   (quotient, remainder) = number / factor
    jnz _factor_not_divisible, c # if (remainder == 0) {
    call write                   #   printf("%llu\n", factor)
    mov n, b                     #   number = quotient
    jmp _factor_rest_loop
_factor_not_divisible:               # } else {
    leu c, b, a
    jnz _factor_print_last, c    #   if quotient < a, print n and return.
    add a, a, 2                  #   else a += 2 }
    jmp _factor_rest_loop # } while (0)
_factor_print_last:
    mov a, n
    call write # printf("%llu", n)
_factor_ret:
    ret


# Read stdin. Must be one decimal string, ending with a newline.
# Behavior on invalid input is unspecified.
# Return value stored in a.
read:
    mov a, 0
_read_loop_start:                # do {
    lw c, 0xffffffffffffffff #   c = getchar()
    sub b, c, ord('\n')
    jz _read_ret, b          #   if (c == '\n'), return
    sub c, c, ord('0')       #   c -= '0'
    mulu a, y, a, 10
    add a, a, c              #   a = 10*a + c
    jmp _read_loop_start     # } while (0)
_read_ret:
    ret a

# Write number in register a to stdout, followed by a newline.
# Fortunately, a 64-bit number has at most 20 digits, and we have 25 registers.
# So we can keep them in registers instead of pushing them onto the stack or heap,
# avoiding the fairly expensive read back.
write:
    divu a, b, a, 10
    jz _write_b, a  
    divu a, c, a, 10
    jz _write_c, a  
    divu a, d, a, 10
    jz _write_d, a  
    divu a, e, a, 10
    jz _write_e, a  
    divu a, f, a, 10
    jz _write_f, a  
    divu a, g, a, 10
    jz _write_g, a  
    divu a, h, a, 10
    jz _write_h, a  
    divu a, i, a, 10
    jz _write_i, a  
    divu a, j, a, 10
    jz _write_j, a  
    divu a, k, a, 10
    jz _write_k, a  
    divu a, l, a, 10
    jz _write_l, a  
    divu a, m, a, 10
    jz _write_m, a  
    divu a, n, a, 10
    jz _write_n, a  
    divu a, o, a, 10
    jz _write_o, a  
    divu a, p, a, 10
    jz _write_p, a  
    divu a, q, a, 10
    jz _write_q, a  
    divu a, r, a, 10
    jz _write_r, a  
    divu a, s, a, 10
    jz _write_s, a  
    divu a, t, a, 10
    jz _write_t, a  
    add a, a, ord('0')
    sw 0xffffffffffffffff, a
_write_t:
    add t, t, ord('0')  
    sw 0xffffffffffffffff, t
_write_s:
    add s, s, ord('0')  
    sw 0xffffffffffffffff, s
_write_r:
    add r, r, ord('0')  
    sw 0xffffffffffffffff, r
_write_q:
    add q, q, ord('0')  
    sw 0xffffffffffffffff, q
_write_p:
    add p, p, ord('0')  
    sw 0xffffffffffffffff, p
_write_o:
    add o, o, ord('0')  
    sw 0xffffffffffffffff, o
_write_n:
    add n, n, ord('0')  
    sw 0xffffffffffffffff, n
_write_m:
    add m, m, ord('0')  
    sw 0xffffffffffffffff, m
_write_l:
    add l, l, ord('0')  
    sw 0xffffffffffffffff, l
_write_k:
    add k, k, ord('0')  
    sw 0xffffffffffffffff, k
_write_j:
    add j, j, ord('0')  
    sw 0xffffffffffffffff, j
_write_i:
    add i, i, ord('0')  
    sw 0xffffffffffffffff, i
_write_h:
    add h, h, ord('0')  
    sw 0xffffffffffffffff, h
_write_g:
    add g, g, ord('0')  
    sw 0xffffffffffffffff, g
_write_f:
    add f, f, ord('0')  
    sw 0xffffffffffffffff, f
_write_e:
    add e, e, ord('0')  
    sw 0xffffffffffffffff, e
_write_d:
    add d, d, ord('0')  
    sw 0xffffffffffffffff, d
_write_c:
    add c, c, ord('0')  
    sw 0xffffffffffffffff, c
_write_b:
    add b, b, ord('0')  
    sw 0xffffffffffffffff, b
    sw 0xffffffffffffffff, ord('\n')
    ret
# End of write.

Full output from my timing loop, in case anyone wants to check the results and/or my copy-paste and math.

13
23
31
37
41
47
47
59
61
79
Execution terminated after 1148 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  0.09s user 0.02s system 94% cpu 0.115 total
2
2
2
2
3
3
107
1121707
164546579
Execution terminated after 9535194 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  55.03s user 0.07s system 99% cpu 55.136 total
3
3
3
7
7
7
13
50759273983933
Execution terminated after 60559378 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  351.38s user 0.32s system 99% cpu 5:51.89 total
7
7
7
13
2531
4091
250250521
Execution terminated after 135135 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  0.84s user 0.01s system 99% cpu 0.857 total
31
89
97
3881
18211
357653
Execution terminated after 155407 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  0.98s user 0.01s system 99% cpu 0.997 total
2
2
2
3
702924188994286579
Execution terminated after 7126449414 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  43067.49s user 86.38s system 99% cpu 12:04:12.58 total
7
103
727
7209485975851
Execution terminated after 22823483 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  134.60s user 0.13s system 99% cpu 2:14.83 total
66449
1604167
1920043
Execution terminated after 13635943 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  81.02s user 0.06s system 99% cpu 1:21.12 total
322255481
52528036667
Execution terminated after 2739172134 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  16119.02s user 12.31s system 99% cpu 4:29:03.61 total
9929766466606501253
Execution terminated after 26784802677 cycles with exit code 0.
/usr/local/bin/golf.py factor.bin <<< $num  156158.25s user 186.81s system 49% cpu 88:35:03.65 total
\$\endgroup\$
10
  • \$\begingroup\$ I tried a C# program using this same basic algorithm. Same numbers, runtime < 2min. How slow is Golf? \$\endgroup\$
    – edc65
    Apr 27 '15 at 16:30
  • \$\begingroup\$ @edc65 Quite slow. I actually wrote a c version first to go off of, it did the largest one in under 30 seconds, the largest completed by golf so far in 7.5. \$\endgroup\$
    – Kevin
    Apr 27 '15 at 16:33
  • \$\begingroup\$ Also, you'll note that 1 GHz is a billion cycles per second, so at full processor speed (2-3GHz) the 10B cycles measured so far would have completed in more like 3-5 seconds instead of 16 hours. \$\endgroup\$
    – Kevin
    Apr 27 '15 at 16:34
  • 1
    \$\begingroup\$ @Kevin take a look at the examples in the github repository - I updated the number input/output to use the callstack, which is only 1 cycle/digit overhead over your hardcoded version :) Also, if you want real speed you can use this to remove the divu: stackoverflow.com/questions/5558492/… . As for your answer - this question was not intended to be solved using trial division :P \$\endgroup\$
    – orlp
    Apr 27 '15 at 20:00
  • \$\begingroup\$ You can speed up your algorithm a lot by checking if factor * factor < number - no number can have factors greater than the square root. \$\endgroup\$
    – orlp
    Apr 27 '15 at 20:05
5
\$\begingroup\$

score = 378,867,816 cycles

[randomized - your results may vary]

Uses the Miller-Rabin primality test (a deterministic version that can handle up to 2^64), a bit of trial factoring, and ECM factoring. All the algebraic operations are in there, including modular addition, subtraction, multiplication, exponentiation, and inversion (mod n<2^64).

Modular multiplication is suboptimal - it does a binary search for the quotient. Computing the remainder of a 128 by 64 divide is tough without a matching builtin instruction. Speed that up and the whole thing will go faster.

2290 bytes compiled

    step = i
    test = j
    tmp  = k

# prints factors of number on stdin, one per line in arbitrary order, to stdout
main:
    call    read_int
    mov a, x
two:
    # remove factors of 2
    and tmp, a, 1
    jnz odd, tmp
    mov x, 2
    call    write_int
    sw  -1, ord('\n')
    shr a, a, 1
    jmp two
odd:
    cmp tmp, a, 1
    jnz done2, tmp
    call    factorodd
done2:
    halt    0

# a = input value >= 3 and odd.  Prints factors of a and returns.
factorodd:
    call    isprime
    jnz prime2, b
    # n is composite.  Try to find a (not necessarily prime) factor.
    call    trial
    jnz split, b
    call    primepower
    jnz split, b
    call    ecm
split:
    # recurse on two parts
    mov a, b
    call    factorodd
    mov a, c
    jmp factorodd
prime2:
    mov x, a
    call    write_int
    sw  -1, ord('\n')
    ret

# a = input value >= 3 and odd.
# b, c = output values, a = b*c, b,c > 1.
# returns b=0 if failure.
trial:
    mov b, 3
loop5:
    divu    c, r, a, b
    jz  found, r
    add b, b, 2
    leu tmp, b, 1001        # TODO: tune max size
    jnz loop5, tmp
    mov b, 0
found:
    ret b, c

# a = input value >= 3.  Must be odd and have >=2 distinct prime factors.
# b, c = output values, a = b*c, b,c > 1.
ecm:
    mov n, a
loop12:
    # choose a random elliptic curve by picking m with 0 <= m < n
    # y^2 = x^3 + mx + 1
    rand    a
    mov b, 1
    mov c, n
    call    mulmod
    mov m, d
    # check that the descriminant is nonzero.  D = 4m^3+27
    mov a, m
    mov b, m
    call    mulmod
    mov a, d
    call    mulmod
    mov a, d
    mov b, 4
    call    mulmod
    mov a, d
    mov b, 27
    call    addmod
    jz  loop12, d
    # try to find factor of n with this elliptic curve
    call    ecmtry
    jz  loop12, b
    divu    c, tmp, n, b
    ret b, c

# n = modulus
# m = curve param
# b = return value - 0 or a factor of n
ecmtry:    
    mov p, 0
    mov q, 1

    # multiply by 2
    mov e, p
    mov f, q
    mov g, p
    mov h, q
    call    ellipticadd
    jnz foundfactor2, d
    mov p, b
    mov q, c

    # continue multiplying by odd numbers
    # TODO: just multiply by odd primes
    mov i, 3
loop15:
    mov e, p
    mov f, q
    mov g, i
    call    ellipticmul
    jnz foundfactor3, d
    mov p, b
    mov q, c
    add i, i, 2
    jnz loop15, p
    jnz loop15, q
    mov b, 0
    ret b
foundfactor3:
    mov b, d
    ret b

# multiplication by a constant in the elliptic curve "group"
#   m = input curve parameter
#   n = input modulus
# e,f = input x,y of point
#   g = input multiplier
# b,c = output x,y of sum
#   d = output 0 if successful, factor of n if not.
ellipticmul:
    # compute g*(e,f) by repeated doubling
    mov x, e
    mov y, f
    mov t, g
    mov r, 0
    mov s, 0
loop14:
    jz  done6, t
    and tmp, t, 1
    jz  noadd, tmp
    # r += x
    mov e, r
    mov f, s
    mov g, x
    mov h, y
    call    ellipticadd
    jnz foundfactor2, d
    mov r, b
    mov s, c
noadd:
    # x += x
    mov e, x
    mov f, y
    mov g, x
    mov h, y
    call    ellipticadd
    jnz foundfactor2, d
    mov x, b
    mov y, c

    shr t, t, 1
    jmp loop14
done6:
    mov b, r
    mov c, s
    mov d, 0
    ret b, c, d
foundfactor2:
    ret d

# addition in the elliptic curve "group"
#   m = input curve parameter
#   n = input modulus
# e,f = input x,y of first point (p)
# g,h = input x,y of second point (q)
# b,c = output x,y of sum
#   d = output 0 if successful, factor of n if not.
ellipticadd:
    px = e
    py = f
    qx = g
    qy = h
    rx = b
    ry = c
    gcd = d
    # 0+q=q
    or  tmp, px, py
    jz  retq, tmp

    # p+0=p
    or  tmp, qx, qy
    jz  retp, tmp

    cmp tmp, px, qx
    jz  diffx, tmp
    cmp tmp, py, qy
    jz  inf, tmp    # px == qx, py != qy, return inf
    jz  inf, py     # px == qx, py == qy, py==0, return inf

    # px == qx, py == qy, py != 0.  This is the double-root case

    # u = numerator = 3 px^2 + a
    mov a, px
    mov b, px
    mov c, n
    call    mulmod
    mov a, d
    mov b, 3
    call    mulmod
    mov a, d
    mov b, m
    call    addmod
    mov u, d

    # v = denominator = 2y
    mov a, py
    mov b, py
    call    addmod
    mov v, d
    jmp divide

diffx:
    # px != qx
    mov a, py
    mov b, qy
    call    submod
    mov u, d        # u = numerator = py - qy

    mov a, px
    mov b, qx
    call    submod
    mov v, d        # v = denominator = px - qx

divide:
    mov a, v
    call    inv
    cmp tmp, c, 1   # gcd(v,n)==1?
    jz  foundfactor, tmp
    mov v, d

    # compute s = u/v mod n = u * v^-1 mod n
    mov a, u
    mov b, v
    mov c, n
    call    mulmod
    mov s, d

    # compute x = s*s - px - qx
    mov a, s
    mov b, s
    call    mulmod
    mov a, d
    mov b, px
    call    submod
    mov a, d
    mov b, qx
    call    submod
    mov x, d

    # compute y = s * (px - x) - py
    mov a, px
    mov b, x
    call    submod
    mov a, d
    mov b, s
    call    mulmod
    mov a, d
    mov b, py
    call    submod

    # return [s*s-px-qx, s*(px-x)-py]
    mov rx, x
    mov ry, d
    mov gcd, 0
    ret rx, ry, gcd

retp:
    mov rx, px
    mov ry, py
    mov gcd, 0
    ret rx, ry, gcd
retq:
    mov rx, qx
    mov ry, qy
    mov gcd, 0
    ret rx, ry, gcd
inf:
    mov rx, 0
    mov ry, 0
    mov gcd, 0
    ret rx, ry, gcd
foundfactor:
    mov gcd, c
    ret gcd

# a = input value >= 3.  Must be odd.
# b = output factor of a.
# if a is a prime power, returns a factor of a.
# otherwise, returns 0.
primepower:
    mov e, 2
loop6:
    mov b, e
    call    nthroot
    leu tmp, c, 3
    jnz notprimepower, tmp

    # compute c^e
    mov r, 1
    mov b, e
loop9:
    mulu    r, tmp, r, c
    dec b
    jnz loop9, b

    cmp tmp, r, a
    jnz isprimepower, tmp

    inc e
    cmp tmp, e, 41  # largest odd power in 2^64 is 3^40
    jz  loop6, tmp
    ret

isprimepower:
    mov b, c
    ret

notprimepower:
    mov b, 0
    ret b

# a = input value
# b = input exponent
# c = output floor(a**(1/b))
nthroot:
    # binary search for the root
    mov c, 0
    mov step, 0x80000000

loop7:
    jz  done3, step
    add test, c, step
    shr step, step, 1

    # check if test^b > a
    # test^b might overflow, so we can't just compute that and compare.
    # so we start with e=a, divide by test b times, and check that
    # the result is 0.
    mov d, b
    mov e, a
loop8:
    divu    e, tmp, e, test
    dec d
    jnz loop8, d

    jz  loop7, e    # test is too big, don't change c

    mov c, test     # test is <= floor(a**(1/b)).  Keep it.
    jmp loop7

done3:
    ret c

# a = input number >= 2
# b = ouput 1/0 if a is prime/composite
isprime:
    # small primes (tests below require that we check these first)
    cmp tmp, a, 2
    jnz prime, tmp
    cmp tmp, a, 3
    jnz prime, tmp
    cmp tmp, a, 5
    jnz prime, tmp
    cmp tmp, a, 7
    jnz prime, tmp
    cmp tmp, a, 11
    jnz prime, tmp
    cmp tmp, a, 13
    jnz prime, tmp
    cmp tmp, a, 17
    jnz prime, tmp
    cmp tmp, a, 19
    jnz prime, tmp
    cmp tmp, a, 23
    jnz prime, tmp
    cmp tmp, a, 29
    jnz prime, tmp
    cmp tmp, a, 31
    jnz prime, tmp
    cmp tmp, a, 37
    jnz prime, tmp

    # even numbers
    and tmp, a, 1
    jz  composite, tmp

    # uses Miller-Rabin with enough fixed bases to guarantee the
    # correct result for numbers up to 2^64.
    # see http://oeis.org/A014233
    mov b, 2
    call    miller_rabin
    jz  composite, c
    mov b, 3
    call    miller_rabin
    jz  composite, c
    mov b, 5
    call    miller_rabin
    jz  composite, c
    mov b, 7
    call    miller_rabin
    jz  composite, c
    mov b, 11
    call    miller_rabin
    jz  composite, c
    mov b, 13
    call    miller_rabin
    jz  composite, c
    mov b, 17
    call    miller_rabin
    jz  composite, c
    mov b, 19
    call    miller_rabin
    jz  composite, c
    mov b, 23
    call    miller_rabin
    jz  composite, c
    mov b, 29
    call    miller_rabin
    jz  composite, c
    mov b, 31
    call    miller_rabin
    jz  composite, c
    mov b, 37
    call    miller_rabin
    jz  composite, c
prime:
    mov b, 1
    ret b
composite:
    mov b, 0
    ret b

# a = input number >= 3
# b = input base value (1 < b < a-1)
# c = output 1 = may be prime, 0 = definitely composite
miller_rabin:
    mov p, a
    mov t, b

    sub q, p, 1
    mov s, 0
    sub e, a, 1
loop2:
    and tmp, e, 1
    jnz endloop2, tmp
    add s, s, 1
    shr e, e, 1
    jmp loop2
endloop2:
    mov a, t
    mov b, e
    mov c, p
    call    pow
    cmp tmp, d, 1
    jnz unknown, tmp
    cmp tmp, d, q
    jnz unknown, tmp
    mov x, d

loop4:
    sub s, s, 1
    jz  composite2, s
    mov a, x
    mov b, x
    mov c, p
    call    mulmod
    cmp tmp, d, 1
    jnz composite2, tmp
    cmp tmp, d, q
    jnz unknown, tmp
    mov x, d
    jmp loop4

composite2:
    mov c, 0
    ret c
unknown:
    mov c, 1
    ret c

# a = input value
# n = input modulus
# returns c, d such that
# c = gcd(a,n)
# d * a % n == gcd(a,n)
inv:
    # extended euclidean algorithm, from
    # http://stackoverflow.com/a/14093613/180090
    new = e
    old = f
    pos = g

    mov p, n
    mov new, 1
    mov old, 0
    mov q, p
    mov pos, 0
loop13:
    jz  done5, a
    divu    q, r, q, a
    mulu    h, tmp, q, new
    add h, old, h
    mov old, new
    mov new, h
    mov q, a
    mov a, r
    xor pos, pos, 1
    jmp loop13
done5:
    mov c, q
    jnz positer, pos
    sub old, p, old
positer:
    mov d, old
    ret c, d

# d = a ** b % c
pow:
    mov r, 1
    mov e, b
    mov t, a
    # t ** e % c
loop3:
    jz  endloop3, e
    and tmp, e, 1
    jz  lowbitclear, tmp

    mov a, t
    mov b, r
    call    mulmod  # r = t*r mod c
    mov r, d

lowbitclear:
    shr e, e, 1
    mov a, t
    mov b, t
    call    mulmod  # t = t*t mod c
    mov t, d
    jmp loop3

endloop3:
    mov d, r
    ret d

# d = a * b % c
mulmod:
    # do multiply
    mulu    e, f, a, b

    # binary search for quotient
    mov  q, 0
    mov  step, 0x8000000000000000
loop:
    jz  done, step

    # test = q + step
    add test, q, step
    shr step, step, 1

    # check test*c
    mulu    g, h, test, c
    geu tmp, h, f
    jnz loop, tmp
    leu tmp, h, f
    jnz ok, tmp
    geu tmp, g, e
    jnz loop, tmp
ok:
    # test*c <= a*b.  Use test as the new q.
    mov q, test
    jmp loop

done:
    # q == quotient of (a*b)/c
    mulu    g, h, q, c  # q*c, g+h<<64 should be close to e+f<<64
    sub d, e, g    # remainder
    ret d

# d = (a + b) % n
# requires 0 <= a, b < n
addmod:
    add d, a, b
    leu tmp, d, a   # wrapped 2^64
    jnz overflow, tmp
    leu tmp, d, n   # result less than modulus?
    jnz inrange, tmp
overflow:
    sub d, d, n
inrange:
    ret d

# d = (a - b) % n
# requires 0 <= a, b < n
submod:
    sub d, a, b
    leu tmp, a, b   # below 0?
    jz  nounderflow, tmp
    add d, d, n
nounderflow:
    ret d

read_int:
    mov x, 0
read_int_loop:
    lw c, -1
    cmp q, c, ord("\n")
    jnz read_int_done, q
    sub c, c, ord("0")
    mulu x, d, x, 10
    add x, x, c
    jmp read_int_loop
read_int_done:
    ret x

write_int:
    divu x, m, x, 10
    jz write_int_done, x
    call write_int
write_int_done:
    add m, m, ord("0")
    sw -1, m
    ret

Output:

13
23
31
37
41
47
47
59
61
79
Execution terminated after 799601 cycles with exit code 0.
2
2
2
2
3
3
107
164546579
1121707
Execution terminated after 216769549 cycles with exit code 0.
3
3
3
7
7
7
13
50759273983933
Execution terminated after 939985 cycles with exit code 0.
7
7
7
13
2531
4091
250250521
Execution terminated after 34213849 cycles with exit code 0.
31
89
97
18211
3881
357653
Execution terminated after 9662357 cycles with exit code 0.
2
2
2
3
702924188994286579
Execution terminated after 748732 cycles with exit code 0.
7
103
727
7209485975851
Execution terminated after 912672 cycles with exit code 0.
66449
1920043
1604167
Execution terminated after 38514477 cycles with exit code 0.
322255481
52528036667
Execution terminated after 75568529 cycles with exit code 0.
9929766466606501253
Execution terminated after 738065 cycles with exit code 0.
\$\endgroup\$
1
  • 3
    \$\begingroup\$ You use way more Miller-Rabin bases than needed. You can check the size of the integer and then use one of the sets of bases found here: miller-rabin.appspot.com . \$\endgroup\$
    – orlp
    May 1 '15 at 13:26
3
\$\begingroup\$

2,279,635 cycles—7373 bytes (deterministic)

One-by-one:

robert@unity:~/golf-cpu/factor$ ./test.sh
13
23
31
37
41
47
47
59
61
79
Execution terminated after 1088 cycles with exit code 0.
2
2
2
2
3
3
107
164546579
1121707
Execution terminated after 41325 cycles with exit code 0.
3
3
3
7
7
7
13
50759273983933
Execution terminated after 9413 cycles with exit code 0.
7
7
7
13
250250521
2531
4091
Execution terminated after 22282 cycles with exit code 0.
31
89
97
357653
3881
18211
Execution terminated after 47656 cycles with exit code 0.
2
2
2
3
702924188994286579
Execution terminated after 17423 cycles with exit code 0.
7
103
7209485975851
727
Execution terminated after 15973 cycles with exit code 0.
1920043
66449
1604167
Execution terminated after 153683 cycles with exit code 0.
52528036667
322255481
Execution terminated after 1952229 cycles with exit code 0.
9929766466606501253
Execution terminated after 18563 cycles with exit code 0.
robert@unity:~/golf-cpu/factor$ 

Summary:

robert@unity:~/golf-cpu/factor$ ./test.py factor.golf factors_testset 
binary length: 7373 bytes
10/10 passed in 0:00:08.53 s
2,279,635 cycles (227963.50 average)
(267.14 KCPS average)

       0 ######################################################################
  100000 ########
  200000 
  300000 
  400000 
  500000 
  600000 
  700000 
  800000 
  900000 
 1000000 
 1100000 
 1200000 
 1300000 
 1400000 
 1500000 
 1600000 
 1700000 
 1800000 
 1900000 ########
robert@unity:~/golf-cpu/factor$ 

I use a combination of trial division and the Brent-Pollard rho algorithm for factorization, and table lookup plus Miller-Rabin for primality testing. I'll add some more explanation tomorrow.

Note that because of the character limit on post length, the second data table is truncated. This gist includes the full table.

primes_53 = \
  b'\x03\x05\x07\x0b\x0d\x11\x13\x17\x1d\x1f\x25\x29\x2b\x2f\x35\x3b' \
  b'\x3d\x43\x47\x49\x4f\x53\x59\x61\x65\x67\x6b\x6d\x71\x7f\x83\x89' \
  b'\x8b\x95\x97\x9d\xa3\xa7\xad\xb3\xb5\xbf\xc1\xc5\xc7\xd3\xdf\xe3' \
  b'\xe5\xe9\xef\xf1\xfb'

# for 2**16+1:2:2**17-1, 1 if prime, 0 otherwise
prime_bytes = \
  b'\x8b\x24\x60\x82\x10\x41\x81\x12\x40\x08\x26\x0d\x03\x00\x01\x41' \
  ...
  b'\x41\x30\x20\x10\x00\x00\x80\x00\x40\x50\x24\x00\x83\x00\x01\x8a'

main:
  call input

# check if input is 1
  cmp c, n, 1
  sz c, 3
    mov o, n
    call print
    halt 0

# remove factors of two  
  mov o, 2
  div_2_loop:
    and c, n, 1
    snz c, 3
      call print
      shr n, n, 1
      jmp div_2_loop

# check if n is a power of two
  cmp c, n, 1
  sz c, 1
    halt 0

# trial division  
  mov d, data(primes_53)
  mov i, 53

  trial_division_loop:
    lbu p, d
    trial_division_check:
      divu q, r, n, p
      snz r, 4
        mov o, p
        call print
        mov n, q
        jmp trial_division_check
    mulu s, t, p, p
    leu c, n, s
    sz c, 5
      cmp c, n, 1
      snz c, 2
        mov o, n
        call print
      halt 0
    sub i, i, 1
    add d, d, 1
    jnz trial_division_loop, i

  # mov g, 0  # initialize factor list pointers
  # mov h, 0  # all registers are zero at program start

  # *g is the next factor to check for primality
  # *h is the last factor we've found so far
  # the first factor is always *0

  sw g, n

prime_test:

  # by this point we know that n has no prime factors less than 256,
  # so if n is less than 256**2, then it must be prime
  lequ c, n, 2**16
  jnz is_prime, c

  geu c, n, 2**17+1
  jnz miller_rabin, c

  sub d, n, 2**16+1  # table starts at 2**16+1 (by above argument)
  shr d, d, 1  # we know n is odd, so we ignore the last bit
  and m, d, 2**3-1  # each byte is 3-bit lookup table
  shr d, d, 3
  add d, d, data(prime_bytes)
  lbu p, d
  shr p, p, m
  and p, p, 1
  jnz is_prime, p

  jmp pollard_rho  # I should probably do trial division here
                   # since we only have around 20 more primes to check

################
# Miller-Rabin primality test; bases from https://miller-rabin.appspot.com/
# Note that this subroutine, as well as most of the ones before the 'utility
# functions' section are not proper functions, as they sometimes jump directly
# to the next step instead of returning!
#
# input: n
# output: n/a
################
miller_rabin:
  shr d, n, 1
  mov b, 1
  mr_rd_loop:  # n - 1 == d * 2**b, d is odd
    and c, d, 1
    snz c, 3
      shr d, d, 1
      inc b
      jmp mr_rd_loop

  geu c, n, 2**32-1  # test if we can use single-precision arithmetic
  jnz miller_rabin_montgomery, c

  sub m, n, 1

  mr_test_1:
    gequ c, n, 0x000000000005361b
    jnz mr_test_2, c

    mov a, 0x81b33f22efdceaa9
    call miller_rabin_test

    jmp is_prime

  mr_test_2:
    gequ c, n, 0x000000003e9de64d
    jnz mr_test_3, c

    mov a, 0x0000004e69b6552d
    call miller_rabin_test

    mov a, 0x00223f5bb83fc553
    call miller_rabin_test

    jmp is_prime

  mr_test_3:
    mov a, 0x3ab4f88ff0cc7c80
    call miller_rabin_test

    mov a, 0xcbee4cdf120c10aa
    call miller_rabin_test

    mov a, 0xe6f1343b0edca8e7
    call miller_rabin_test

    jmp is_prime

miller_rabin_montgomery:
  call montgomery_precompute
  sub m, n, r  # montgomery representation of n-1

  mr_test_mt_3:
    gequ c, n, 0x000000518dafbfd1
    jnz mr_test_mt_4, c

    mov a, 0x3ab4f88ff0cc7c80
    call miller_rabin_test_montgomery

    mov a, 0xcbee4cdf120c10aa
    call miller_rabin_test_montgomery

    mov a, 0xe6f1343b0edca8e7
    call miller_rabin_test_montgomery

    jmp is_prime

  mr_test_mt_4:
    gequ c, n, 0x0000323ee0e55e6b
    jnz mr_test_mt_5, c

    mov a, 0x0000000000000002
    call miller_rabin_test_montgomery

    mov a, 0x0000810c207b08bf
    call miller_rabin_test_montgomery

    mov a, 0x10a42595b01d3765
    call miller_rabin_test_montgomery

    mov a, 0x99fd2b545eab5322
    call miller_rabin_test_montgomery

    jmp is_prime

  mr_test_mt_5:
    gequ c, n, 0x001c6b470864f683
    jnz mr_test_mt_6, c

    mov a, 0x0000000000000002
    call miller_rabin_test_montgomery

    mov a, 0x000003c1c7396f6d
    call miller_rabin_test_montgomery

    mov a, 0x02142e2e3f22de5c
    call miller_rabin_test_montgomery

    mov a, 0x0297105b6b7b29dd
    call miller_rabin_test_montgomery

    mov a, 0x370eb221a5f176dd
    call miller_rabin_test_montgomery

    jmp is_prime

  mr_test_mt_6:
    gequ c, n, 0x081f23f390affe89
    jnz mr_test_mt_7, c

    mov a, 0x0000000000000002
    call miller_rabin_test_montgomery

    mov a, 0x000070722e8f5cd0
    call miller_rabin_test_montgomery

    mov a, 0x0020cd6bd5ace2d1
    call miller_rabin_test_montgomery

    mov a, 0x009bbc940c751630
    call miller_rabin_test_montgomery

    mov a, 0x0a90404784bfcb4d
    call miller_rabin_test_montgomery

    mov a, 0x1189b3f265c2b0c7
    call miller_rabin_test_montgomery

    jmp is_prime

  mr_test_mt_7:
    mov a, 0x0000000000000002
    call miller_rabin_test_montgomery

    mov a, 0x0000000000000145
    call miller_rabin_test_montgomery

    mov a, 0x000000000000249f
    call miller_rabin_test_montgomery

    mov a, 0x0000000000006e12
    call miller_rabin_test_montgomery

    mov a, 0x000000000006e0d7
    call miller_rabin_test_montgomery

    mov a, 0x0000000000953d18
    call miller_rabin_test_montgomery

    mov a, 0x000000006b0191fe
    call miller_rabin_test_montgomery

    jmp is_prime

  is_prime:
    mov o, n
    call print
    cmp c, g, h
    sz c, 1
      halt 0
    add g, g, 8
    lw n, g
    jmp prime_test

  found_factor:
    divu n, b, n, a 
    add h, h, 8
    sw h, a
    jmp prime_test

################
# Miller-Rabin primality test subroutine; needs m == n - 1
#
# input: a, n, m
# output: n/a
################
miller_rabin_test:
  divu q, a, a, n  # a = a mod n
  snz a, 1
    ret  # a certifies primality if a == 0 mod n
  call power  # a = a**d mod n
  cmp c, a, 1  # r == 1
  sz c, 1
    ret  # a certifies primality if a**d == 1 mod n
  cmp c, a, m  # m == n-1
  sz c, 1
    ret  # a certifies primality if a**d == -1 mod n

  mov d, 2
  mr_square_loop:
    dec b
    jz pollard_rho, b
    mulu x, y, a, a  # a = a**2 mod n
    divu q, a, x, n  # q is unused
    cmp c, a, 1  # r == 1
    jnz pollard_rho, c  # a witnesses compositeness if a**(d*2**i) == 1 mod n
    cmp c, a, m  # m == n-1
    sz c, 1
      ret  # a certifies primality if a**(d*2**i) == -1 mod n
    jmp mr_square_loop

################
# Miller-Rabin primality test subroutine using Montgomery arithmetic; needs
# the values from the precomputation step as well as m == n - 1
#
# input: a, n, m, (u, v, r, s)
# output: n/a
################
miller_rabin_test_montgomery:
  divu q, a, a, n  # a = a mod n
  snz a, 1
    ret  # a certifies primality if a == 0 mod n
  mulu x, y, a, s
  call montgomery_reduce  # convert a to montgomery form
  mov a, x
  call montgomery_power  # a = a**d mod n
  cmp c, a, r  # r == 1 (mongtomery form)
  sz c, 1
    ret  # a certifies primality if a**d == 1 mod n
  cmp c, a, m  # m == n-1 (montgomery form)
  sz c, 1
    ret  # a certifies primality if a**d == -1 mod n

  mr_mt_square_loop:
    dec b
    jz pollard_rho_montgomery, b
    mulu x, y, a, a  # a = a**2 mod n
    call montgomery_reduce
    mov a, x
    cmp c, a, r  # r == 1 (mongtomery form)
    jnz pollard_rho_montgomery, c  # a witnesses compositeness if a**(d*2**i) == 1 mod n
    cmp c, a, m  # m == n-1 (montgomery form)
    sz c, 1
      ret  # a certifies primality if a**(d*2**i) == -1 mod n
    jmp mr_mt_square_loop

################
# Pollard-Brent rho factorization algorithm
#
# input: n
# output: n/a
################
pollard_rho:

  rho_skip_count = 64

  mov o, 42
  rho_retry:

  mov b, o
  mov j, 1
  mov f, 1
  mov d, 1
  rho_outer_loop:
  mov a, b
    mov i, j
    rho_fast_loop:
      mulu b, y, b, b
      add b, b, 1
      divu y, b, b, n
      #mov o, b
      #call print
      sub i, i, 1
      jnz rho_fast_loop, i
    mov k, 0
    rho_slow_loop:
      mov e, b
      sub i, j, k
      leu c, rho_skip_count, i
      sz c, 1
        mov i, rho_skip_count
      rho_inner_loop:
        mulu b, y, b, b
        add b, b, 1
        divu y, b, b, n
        leu c, a, b
        sz c, 1
          sub x, b, a
        snz c, 1
          sub x, a, b
        mulu f, y, x, f
        divu y, f, f, n
        #add o, f, 1000000000
        #call print
        sub i, i, 1
        jnz rho_inner_loop, i
      mov x, f
      call gcd
      mov d, x
      #mov o, d
      #call print
      add k, k, rho_skip_count
      gequ c, k, j
      snz c, 2
        lequ c, d, 1
        jnz rho_slow_loop, c
    shl j, j, 1
  lequ c, d, 1
  jnz rho_outer_loop, c

  cmp c, d, n
  sz c, 12
    rho_final_loop:
      mulu e, y, e, e
      add e, e, 1
      divu y, e, e, n
      #add o, e, 2000000000
      #call print
      leu c, a, e
      sz c, 1
        sub x, e, a
      snz c, 1
        sub x, a, e
      call gcd
      mov d, x
      #mov o, d
      #call print
      lequ c, d, 1
      jnz rho_final_loop, c

  cmp c, d, n
  sz c, 2
    add o, o, 1
    jmp rho_retry

  mov a, d
  jmp found_factor


################
# Pollard-Brent rho factorization algorithm using Montgomery arithmetic.
# Requires m = n - r
#
# input: n, (u, v, r, s, m)
# output: n/a
################
pollard_rho_montgomery:

  rho_mt_skip_count = 64

  mov o, 42
  rho_mt_retry:

  mulu x, y, o, s
  call montgomery_reduce
  mov b, x
  mov j, 1
  mov f, r
  mov d, 1
  rho_mt_outer_loop:
  mov a, b
    mov i, j
    rho_mt_fast_loop:
      mulu x, y, b, b
      call montgomery_reduce
      mov b, x
      geu c, b, m
      sz c, 1
        sub b, b, m
      snz c, 1
        add b, b, r
      #mov o, b
      #call print
      sub i, i, 1
      jnz rho_mt_fast_loop, i
    mov k, 0
    rho_mt_slow_loop:
      mov e, b
      sub i, j, k
      leu c, rho_mt_skip_count, i
      sz c, 1
        mov i, rho_mt_skip_count
      rho_mt_inner_loop:
        mulu x, y, b, b
        call montgomery_reduce
        mov b, x
        geu c, b, m
        sz c, 1
          sub b, b, m
        snz c, 1
          add b, b, r
        leu c, a, b
        sz c, 1
          sub x, b, a
        snz c, 1
          sub x, a, b
        mulu x, y, x, f
        call montgomery_reduce
        mov f, x
        sub i, i, 1
        jnz rho_mt_inner_loop, i
      mov x, f
      #mov o, x
      #call print
      call gcd
      mov d, x
      #mov o, d
      #call print
      add k, k, rho_mt_skip_count
      gequ c, k, j
      snz c, 2
        lequ c, d, 1
        jnz rho_mt_slow_loop, c
    shl j, j, 1
  lequ c, d, 1
  jnz rho_mt_outer_loop, c

  cmp c, d, n
  sz c, 15
    rho_mt_final_loop:
      mulu x, y, e, e
      call montgomery_reduce
      mov e, x
      geu c, e, m
      sz c, 1
        sub e, e, m
      snz c, 1
        add e, e, r
      leu c, a, e
        sz c, 1
          sub x, e, a
        snz c, 1
          sub x, a, e
      call gcd
      mov d, x
      lequ c, d, 1
      jnz rho_mt_final_loop, c

  cmp c, d, n
  sz c, 2
    add o, o, 1
    jmp rho_mt_retry

  mov a, d
  jmp found_factor

################ UTILITY FUNCTIONS ################

################
# Loads a decimal number terminated by a newline from stdin to register n.
#
# inputs:  none
# outputs: n
################
input:
  lw c, -1
  input_add_digit:
    sub c, c, ord('0')
    mov o, c
    mulu n, h, n, 10
    add n, n, c
    lw c, -1
    cmp q, c, ord('\n')
    jz input_add_digit, q
  ret n


################
# Prints the value of register o to stdout in decimal, followed by a newline.
#
# inputs:  o
# outputs: none
################
print:
  call print_char
  sw -1, ord('\n')
  ret

  print_char:
    divu o, x, o, 10
    sz o, 1
      call print_char
    add x, x, ord('0')
    sw -1, x
    ret

################
# Precomputes values used for Montgomery multiplication:
#  * u = 1/2**64 mod n
#  * v = -1/n mod 2**64
#  * r = 2**64 mod n  (montgomery representation of 1)
#  * s = 2**128 mod n (montgomery representation of 2**64)
#
# inputs: n
# outputs: u, v, s, t
################
montgomery_precompute:
  # first compute the inverses; based on xbinGCD from
  # http://www.hackersdelight.org/MontgomeryMultiplication.pdf
  # This step takes something like an average of 7 cycles per bit in the
  # 'fast' mode, and 8 cycles per bit in 'safe' mode, for a total of around
  # 500 cycles: but we only have to do it once per modulus

  mov u, 1
  mov v, 0
  mov i, 64
  # HD defensively computes (u+beta)/2 to avoid overflow, taking two extra
  # instructions; however, since u < beta overflow is only possible when
  # beta >= 2**63, in most cases we can use a faster version and save
  # 2 * 64 = 128 cycles, at the expense of a couple cycles comparison
  gequ c, n, 2**63
  jz mt_pre_gcd_loop, c
  mt_pre_gcd_loop_safe:
    dec i
    and c, u, 1
    snz c, 3
      shr u, u, 1
      shr v, v, 1
    sz 0, 6
      and c, u, n
      xor u, u, n
      shr u, u, 1
      add u, u, c
      shr v, v, 1
      add v, v, 2**63   
    jnz mt_pre_gcd_loop_safe, i
    jmp mt_pre_gcd_end
  mt_pre_gcd_loop:
    dec i
    and c, u, 1
    snz c, 3
      shr u, u, 1
      shr v, v, 1
    sz 0, 4
      add u, u, n
      shr u, u, 1
      shr v, v, 1
      add v, v, 2**63
    jnz mt_pre_gcd_loop, i
  mt_pre_gcd_end:

  # compute 2**64 mod n; since 2**64 is too large to fit in a register, we
  # first calculate r = 2**63 mod n, if it's greater than n/2, r = 2r - n,
  # otherwise just r = 2r

  divu q, r, 2**63, n # q is unused
  shr c, n, 1
  geu c, r, c
  shl r, r, 1
  sz c, 1
    sub r, r, n

  # It would be entirely possible to compute 2**128 mod n by starting with
  # r and using repeated doubling (64 times); this would take something
  # like 4*64 = 256 cycles.  Instead I'll use a doubleword division
  # algorithm from Hacker's Delight (ch. 9-4, fig. 9-3), which takes
  # fewer than 100 cycles.

  mov l, 0
  # normalize the divisor (n)
  and c, n, 2**64 - 2**32
  snz c, 2
    shl n, n, 32
    add l, l, 32
  and c, n, 2**64 - 2**48
  snz c, 2
    shl n, n, 16
    add l, l, 16
  and c, n, 2**64 - 2**56
  snz c, 2
    shl n, n, 8
    add l, l, 8
  and c, n, 2**64 - 2**60
  snz c, 2
    shl n, n, 4
    add l, l, 4
  and c, n, 2**64 - 2**62
  snz c, 2
    shl n, n, 2
    add l, l, 2
  and c, n, 2**64 - 2**63
  snz c, 2
    shl n, n, 1
    add l, l, 1
  # normalize the numerator
  shl a, r, l
  # split the divisor into halfwords
  shr b, n, 32
  and m, n, 2**32 - 1
  # compute first halfword of remainder
  divu q, p, a, b
  mt_pre_div_adjust1: # loop runs at most two times, 035x on average
    gequ c, q, 2**32
    snz c, 4
      mulu d, f, q, m # f is unused
      shl c, p, 32
      geu c, d, c
      sz c, 4
        sub q, q, 1
        add p, p, b
        leu c, p, 2**32
        jnz mt_pre_div_adjust1, c
  shl a, a, 32
  mulu d, f, q, n
  sub a, a, d
  # compute second halfword of remainder
  divu q, p, a, b
  mt_pre_div_adjust2:
    snz c, 4
      mulu d, f, q, m
      shl c, p, 32
      geu c, d, c
      sz c, 4
        sub q, q, 1
        add p, p, b
        leu c, p, 2**32
        jnz mt_pre_div_adjust2, c
  shl a, a, 32
  mulu d, f, q, n
  sub a, a, d
  # de-normalize remainder
  shr s, a, l

  ret u, v, r, s

################
# Performs the Montgomery reduction step, x = [yx]/2**64 mod n
# Requres the u and v calculated in mongomery_precompute.
#
# inputs: x, y, n, (u, v)
# outputs: x 
################
montgomery_reduce:
  mulu m, u, x, v  # m = ([yx] mod 2**64) / (-n) mod 2**64
  mulu z, w, m, n  # [wz] = mN
  add x, x, z      # [yx] += [wz]
  leu c, x, z      # this is where I really miss an ADC instruction
  sz c, 1
    inc w
  add x, y, w      # x = [yx] / 2**64 = y (combined with y+w from above)
  leu c, x, y      # x -= n if overflow
  sz c, 1
    sub x, x, n
  gequ c, x, n     # if x >= n
  sz c, 1
    sub x, x, n    # x -= n
  ret x

################
# Computes a = a**d mod n by repeated squaring.
#
# inputs: a, d, n
# outputs: a
################
power:
  mov b, a
  mov a, 1
  mt_pow_loop:
    and c, d, 1
    sz c, 2
      mulu x, y, a, b  # a = a*b mod n
      divu q, a, x, n  # q is unused
    mulu x, y, b, b  # b = b*b mod n
    divu q, b, x, n
    shr d, d, 1
    jnz mt_pow_loop, d
  ret a

################
# Uses Montgomery multiplication to compute a = a**d mod n.  Treats d as an
# ordinary unsigned integer; treats d as an integer in Montgomery form.
# Requres the u, v, and r calculated in mongomery_precompute.
#
# inputs: a, d, n, (u, v, r)
# outputs: a 
################
montgomery_power:
  mov b, a
  mov a, r
  pow_loop:
    and c, d, 1
    sz c, 3
      mulu x, y, a, b
      call montgomery_reduce
      mov a, x
    mulu x, y, b, b
    call montgomery_reduce
    mov b, x
    shr d, d, 1
    jnz pow_loop, d
  ret a

################
# Computes x = GCD(x,n) using the binary GCD algorithm.  Assumes that x < n
# and that n is odd.  Note that we don't need a separate Montgomery GCD,
# since, surprisingly, GCD(x*(2**64) mod n, n) == GCD(x, n).
#
# inputs: x, n
# outputs: x
################
gcd:
  snz x, 2  # GCD(0, n) == n
    mov x, n
    ret x

  gcd_loop:
    and c, x, 1  # n is odd, so the GCD has no factors of two
    snz c, 3
    gcd_div_2_loop:  
      shr x, x, 1
      and c, x, 1
      jz gcd_div_2_loop, c

    geu c, n, x
    sz c, 5
      sub x, n, x
      sub n, n, x
      jnz gcd_loop, x
        mov x, n
        ret x      

    sub x, x, n
    jnz gcd_loop, x
      mov x, n
      ret x      
\$\endgroup\$
6
  • \$\begingroup\$ You should definitely include a fully working and testable example, so please do include the table in some way or form. \$\endgroup\$
    – orlp
    Oct 19 '15 at 7:06
  • \$\begingroup\$ @orlp Do you have access to Mathematica? I can easily include the code I used to generate the table. \$\endgroup\$ Oct 19 '15 at 7:08
  • \$\begingroup\$ I do not. I think putting a dump of the full untruncated code on gist.github.com would be fine however. \$\endgroup\$
    – orlp
    Oct 19 '15 at 7:10
  • \$\begingroup\$ As for your implementation, I would recognize my code in my sleep :) The mov o, 42 is a dead giveaway. \$\endgroup\$
    – orlp
    Oct 19 '15 at 7:12
  • \$\begingroup\$ @orlp Thanks for reminding me about gist. And actually, the 42 happens to be a coincidence; I copied the algorithm from the original paper. Great minds think alike and all that... \$\endgroup\$ Oct 19 '15 at 7:16

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