gcc/gmp/mpn/x86/k7/mmx/divrem_1.asm - Issue 3050029: [gcc] GCC 4.5.0=>4.5.1

Unified Diff: gcc/gmp/mpn/x86/k7/mmx/divrem_1.asm

Issue 3050029: [gcc] GCC 4.5.0=>4.5.1 (Closed) Base URL: ssh://git@gitrw.chromium.org:9222/nacl-toolchain.git

Patch Set: Created 10 years, 5 months ago

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Index: gcc/gmp/mpn/x86/k7/mmx/divrem_1.asm

diff --git a/gcc/gmp/mpn/x86/k7/mmx/divrem_1.asm b/gcc/gmp/mpn/x86/k7/mmx/divrem_1.asm

deleted file mode 100644

index fa5824c7b9863da3a1d9eddead7dd3353a17b646..0000000000000000000000000000000000000000

--- a/gcc/gmp/mpn/x86/k7/mmx/divrem_1.asm

+++ /dev/null

@@ -1,821 +0,0 @@

-dnl AMD K7 mpn_divrem_1, mpn_divrem_1c, mpn_preinv_divrem_1 -- mpn by limb

-dnl division.

-dnl

-dnl This file is part of the GNU MP Library.

-dnl

-dnl The GNU MP Library is free software; you can redistribute it and/or

-dnl modify it under the terms of the GNU Lesser General Public License as

-dnl published by the Free Software Foundation; either version 3 of the

-dnl License, or (at your option) any later version.

-dnl

-dnl The GNU MP Library is distributed in the hope that it will be useful,

-dnl but WITHOUT ANY WARRANTY; without even the implied warranty of

-dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

-dnl Lesser General Public License for more details.

-dnl

-dnl You should have received a copy of the GNU Lesser General Public License

-dnl along with the GNU MP Library. If not, see http://www.gnu.org/licenses/.

-include(`../config.m4')

-C K7: 17.0 cycles/limb integer part, 15.0 cycles/limb fraction part.

-C mp_limb_t mpn_divrem_1 (mp_ptr dst, mp_size_t xsize,

-C mp_srcptr src, mp_size_t size,

-C mp_limb_t divisor);

-C mp_limb_t mpn_divrem_1c (mp_ptr dst, mp_size_t xsize,

-C mp_srcptr src, mp_size_t size,

-C mp_limb_t divisor, mp_limb_t carry);

-C mp_limb_t mpn_preinv_divrem_1 (mp_ptr dst, mp_size_t xsize,

-C mp_srcptr src, mp_size_t size,

-C mp_limb_t divisor, mp_limb_t inverse,

-C unsigned shift);

-C

-C Algorithm:

-C

-C The method and nomenclature follow part 8 of "Division by Invariant

-C Integers using Multiplication" by Granlund and Montgomery, reference in

-C gmp.texi.

-C

-C The "and"s shown in the paper are done here with "cmov"s. "m" is written

-C for m', and "d" for d_norm, which won't cause any confusion since it's

-C only the normalized divisor that's of any use in the code. "b" is written

-C for 2^N, the size of a limb, N being 32 here.

-C

-C The step "sdword dr = n - 2^N*d + (2^N-1-q1) * d" is instead done as

-C "n-(q1+1)*d"; this rearrangement gives the same two-limb answer. If

-C q1==0xFFFFFFFF, then q1+1 would overflow. We branch to a special case

-C "q1_ff" if this occurs. Since the true quotient is either q1 or q1+1 then

-C if q1==0xFFFFFFFF that must be the right value.

-C

-C For the last and second last steps q1==0xFFFFFFFF is instead handled by an

-C sbbl to go back to 0xFFFFFFFF if an overflow occurs when adding 1. This

-C then goes through as normal, and finding no addback required. sbbl costs

-C an extra cycle over what the main loop code does, but it keeps code size

-C and complexity down.

-C

-C Notes:

-C

-C mpn_divrem_1 and mpn_preinv_divrem_1 avoid one division if the src high

-C limb is less than the divisor. mpn_divrem_1c doesn't check for a zero

-C carry, since in normal circumstances that will be a very rare event.

-C

-C The test for skipping a division is branch free (once size>=1 is tested).

-C The store to the destination high limb is 0 when a divide is skipped, or

-C if it's not skipped then a copy of the src high limb is used. The latter

-C is in case src==dst.

-C

-C There's a small bias towards expecting xsize==0, by having code for

-C xsize==0 in a straight line and xsize!=0 under forward jumps.

-C

-C Alternatives:

-C

-C If the divisor is normalized (high bit set) then a division step can

-C always be skipped, since the high destination limb is always 0 or 1 in

-C that case. It doesn't seem worth checking for this though, since it

-C probably occurs infrequently, in particular note that big_base for a

-C decimal mpn_get_str is not normalized in a 32-bit limb.

-dnl MUL_THRESHOLD is the value of xsize+size at which the multiply by

-dnl inverse method is used, rather than plain "divl"s. Minimum value 1.

-dnl

-dnl The inverse takes about 50 cycles to calculate, but after that the

-dnl multiply is 17 c/l versus division at 42 c/l.

-dnl

-dnl At 3 limbs the mul is a touch faster than div on the integer part, and

-dnl even more so on the fractional part.

-deflit(MUL_THRESHOLD, 3)

-defframe(PARAM_PREINV_SHIFT, 28) dnl mpn_preinv_divrem_1

-defframe(PARAM_PREINV_INVERSE, 24) dnl mpn_preinv_divrem_1

-defframe(PARAM_CARRY, 24) dnl mpn_divrem_1c

-defframe(PARAM_DIVISOR,20)

-defframe(PARAM_SIZE, 16)

-defframe(PARAM_SRC, 12)

-defframe(PARAM_XSIZE, 8)

-defframe(PARAM_DST, 4)

-defframe(SAVE_EBX, -4)

-defframe(SAVE_ESI, -8)

-defframe(SAVE_EDI, -12)

-defframe(SAVE_EBP, -16)

-defframe(VAR_NORM, -20)

-defframe(VAR_INVERSE, -24)

-defframe(VAR_SRC, -28)

-defframe(VAR_DST, -32)

-defframe(VAR_DST_STOP,-36)

-deflit(STACK_SPACE, 36)

- TEXT

- ALIGN(32)

-PROLOGUE(mpn_preinv_divrem_1)

-deflit(`FRAME',0)

- movl PARAM_XSIZE, %ecx

- movl PARAM_DST, %edx

- subl $STACK_SPACE, %esp FRAME_subl_esp(STACK_SPACE)

- movl %esi, SAVE_ESI

- movl PARAM_SRC, %esi

- movl %ebx, SAVE_EBX

- movl PARAM_SIZE, %ebx

- leal 8(%edx,%ecx,4), %edx C &dst[xsize+2]

- movl %ebp, SAVE_EBP

- movl PARAM_DIVISOR, %ebp

- movl %edx, VAR_DST_STOP C &dst[xsize+2]

- movl %edi, SAVE_EDI

- xorl %edi, %edi C carry

- movl -4(%esi,%ebx,4), %eax C src high limb

- xor %ecx, %ecx

- C

- cmpl %ebp, %eax C high cmp divisor

- cmovc( %eax, %edi) C high is carry if high<divisor

- cmovnc( %eax, %ecx) C 0 if skip div, src high if not

- C (the latter in case src==dst)

- movl %ecx, -12(%edx,%ebx,4) C dst high limb

- sbbl $0, %ebx C skip one division if high<divisor

- movl PARAM_PREINV_SHIFT, %ecx

- leal -8(%edx,%ebx,4), %edx C &dst[xsize+size]

- movl $32, %eax

- movl %edx, VAR_DST C &dst[xsize+size]

- shll %cl, %ebp C d normalized

- subl %ecx, %eax

- movl %ecx, VAR_NORM

- movd %eax, %mm7 C rshift

- movl PARAM_PREINV_INVERSE, %eax

- jmp L(start_preinv)

-EPILOGUE()

- ALIGN(16)

-PROLOGUE(mpn_divrem_1c)

-deflit(`FRAME',0)

- movl PARAM_CARRY, %edx

- movl PARAM_SIZE, %ecx

- subl $STACK_SPACE, %esp

-deflit(`FRAME',STACK_SPACE)

- movl %ebx, SAVE_EBX

- movl PARAM_XSIZE, %ebx

- movl %edi, SAVE_EDI

- movl PARAM_DST, %edi

- movl %ebp, SAVE_EBP

- movl PARAM_DIVISOR, %ebp

- movl %esi, SAVE_ESI

- movl PARAM_SRC, %esi

- leal -4(%edi,%ebx,4), %edi C &dst[xsize-1]

- jmp L(start_1c)

-EPILOGUE()

- C offset 0xa1, close enough to aligned

-PROLOGUE(mpn_divrem_1)

-deflit(`FRAME',0)

- movl PARAM_SIZE, %ecx

- movl $0, %edx C initial carry (if can't skip a div)

- subl $STACK_SPACE, %esp

-deflit(`FRAME',STACK_SPACE)

- movl %esi, SAVE_ESI

- movl PARAM_SRC, %esi

- movl %ebx, SAVE_EBX

- movl PARAM_XSIZE, %ebx

- movl %ebp, SAVE_EBP

- movl PARAM_DIVISOR, %ebp

- orl %ecx, %ecx C size

- movl %edi, SAVE_EDI

- movl PARAM_DST, %edi

- leal -4(%edi,%ebx,4), %edi C &dst[xsize-1]

- jz L(no_skip_div) C if size==0

- movl -4(%esi,%ecx,4), %eax C src high limb

- xorl %esi, %esi

- cmpl %ebp, %eax C high cmp divisor

- cmovc( %eax, %edx) C high is carry if high<divisor

- cmovnc( %eax, %esi) C 0 if skip div, src high if not

- movl %esi, (%edi,%ecx,4) C dst high limb

- sbbl $0, %ecx C size-1 if high<divisor

- movl PARAM_SRC, %esi C reload

-L(no_skip_div):

-L(start_1c):

- C eax

- C ebx xsize

- C ecx size

- C edx carry

- C esi src

- C edi &dst[xsize-1]

- C ebp divisor

- leal (%ebx,%ecx), %eax C size+xsize

- cmpl $MUL_THRESHOLD, %eax

- jae L(mul_by_inverse)

-C With MUL_THRESHOLD set to 3, the simple loops here only do 0 to 2 limbs.

-C It'd be possible to write them out without the looping, but no speedup

-C would be expected.

-C

-C Using PARAM_DIVISOR instead of %ebp measures 1 cycle/loop faster on the

-C integer part, but curiously not on the fractional part, where %ebp is a

-C (fixed) couple of cycles faster.

- orl %ecx, %ecx

- jz L(divide_no_integer)

-L(divide_integer):

- C eax scratch (quotient)

- C ebx xsize

- C ecx counter

- C edx scratch (remainder)

- C esi src

- C edi &dst[xsize-1]

- C ebp divisor

- movl -4(%esi,%ecx,4), %eax

- divl PARAM_DIVISOR

- movl %eax, (%edi,%ecx,4)

- decl %ecx

- jnz L(divide_integer)

-L(divide_no_integer):

- movl PARAM_DST, %edi

- orl %ebx, %ebx

- jnz L(divide_fraction)

-L(divide_done):

- movl SAVE_ESI, %esi

- movl SAVE_EDI, %edi

- movl %edx, %eax

- movl SAVE_EBX, %ebx

- movl SAVE_EBP, %ebp

- addl $STACK_SPACE, %esp

- ret

-L(divide_fraction):

- C eax scratch (quotient)

- C ebx counter

- C ecx

- C edx scratch (remainder)

- C esi

- C edi dst

- C ebp divisor

- movl $0, %eax

- divl %ebp

- movl %eax, -4(%edi,%ebx,4)

- decl %ebx

- jnz L(divide_fraction)

- jmp L(divide_done)

-C -----------------------------------------------------------------------------

-L(mul_by_inverse):

- C eax

- C ebx xsize

- C ecx size

- C edx carry

- C esi src

- C edi &dst[xsize-1]

- C ebp divisor

- bsrl %ebp, %eax C 31-l

- leal 12(%edi), %ebx C &dst[xsize+2], loop dst stop

- leal 4(%edi,%ecx,4), %edi C &dst[xsize+size]

- movl %edi, VAR_DST

- movl %ebx, VAR_DST_STOP

- movl %ecx, %ebx C size

- movl $31, %ecx

- movl %edx, %edi C carry

- movl $-1, %edx

- C

- xorl %eax, %ecx C l

- incl %eax C 32-l

- shll %cl, %ebp C d normalized

- movl %ecx, VAR_NORM

- movd %eax, %mm7

- movl $-1, %eax

- subl %ebp, %edx C (b-d)-1 giving edx:eax = b*(b-d)-1

- divl %ebp C floor (b*(b-d)-1) / d

-L(start_preinv):

- C eax inverse

- C ebx size

- C ecx shift

- C edx

- C esi src

- C edi carry

- C ebp divisor

- C

- C mm7 rshift

- orl %ebx, %ebx C size

- movl %eax, VAR_INVERSE

- leal -12(%esi,%ebx,4), %eax C &src[size-3]

- jz L(start_zero)

- movl %eax, VAR_SRC

- cmpl $1, %ebx

- movl 8(%eax), %esi C src high limb

- jz L(start_one)

-L(start_two_or_more):

- movl 4(%eax), %edx C src second highest limb

- shldl( %cl, %esi, %edi) C n2 = carry,high << l

- shldl( %cl, %edx, %esi) C n10 = high,second << l

- cmpl $2, %ebx

- je L(integer_two_left)

- jmp L(integer_top)

-L(start_one):

- shldl( %cl, %esi, %edi) C n2 = carry,high << l

- shll %cl, %esi C n10 = high << l

- movl %eax, VAR_SRC

- jmp L(integer_one_left)

-L(start_zero):

- C Can be here with xsize==0 if mpn_preinv_divrem_1 had size==1 and

- C skipped a division.

- shll %cl, %edi C n2 = carry << l

- movl %edi, %eax C return value for zero_done

- cmpl $0, PARAM_XSIZE

- je L(zero_done)

- jmp L(fraction_some)

-C -----------------------------------------------------------------------------

-C

-C The multiply by inverse loop is 17 cycles, and relies on some out-of-order

-C execution. The instruction scheduling is important, with various

-C apparently equivalent forms running 1 to 5 cycles slower.

-C

-C A lower bound for the time would seem to be 16 cycles, based on the

-C following successive dependencies.

-C

-C cycles

-C n2+n1 1

-C mul 6

-C q1+1 1

-C mul 6

-C sub 1

-C addback 1

-C ---

-C 16

-C

-C This chain is what the loop has already, but 16 cycles isn't achieved.

-C K7 has enough decode, and probably enough execute (depending maybe on what

-C a mul actually consumes), but nothing running under 17 has been found.

-C

-C In theory n2+n1 could be done in the sub and addback stages (by

-C calculating both n2 and n2+n1 there), but lack of registers makes this an

-C unlikely proposition.

-C

-C The jz in the loop keeps the q1+1 stage to 1 cycle. Handling an overflow

-C from q1+1 with an "sbbl $0, %ebx" would add a cycle to the dependent

-C chain, and nothing better than 18 cycles has been found when using it.

-C The jump is taken only when q1 is 0xFFFFFFFF, and on random data this will

-C be an extremely rare event.

-C

-C Branch mispredictions will hit random occurrances of q1==0xFFFFFFFF, but

-C if some special data is coming out with this always, the q1_ff special

-C case actually runs at 15 c/l. 0x2FFF...FFFD divided by 3 is a good way to

-C induce the q1_ff case, for speed measurements or testing. Note that

-C 0xFFF...FFF divided by 1 or 2 doesn't induce it.

-C

-C The instruction groupings and empty comments show the cycles for a naive

-C in-order view of the code (conveniently ignoring the load latency on

-C VAR_INVERSE). This shows some of where the time is going, but is nonsense

-C to the extent that out-of-order execution rearranges it. In this case

-C there's 19 cycles shown, but it executes at 17.

- ALIGN(16)

-L(integer_top):

- C eax scratch

- C ebx scratch (nadj, q1)

- C ecx scratch (src, dst)

- C edx scratch

- C esi n10

- C edi n2

- C ebp divisor

- C

- C mm0 scratch (src qword)

- C mm7 rshift for normalization

- cmpl $0x80000000, %esi C n1 as 0=c, 1=nc

- movl %edi, %eax C n2

- movl VAR_SRC, %ecx

- leal (%ebp,%esi), %ebx

- cmovc( %esi, %ebx) C nadj = n10 + (-n1 & d), ignoring overflow

- sbbl $-1, %eax C n2+n1

- mull VAR_INVERSE C m*(n2+n1)

- movq (%ecx), %mm0 C next limb and the one below it

- subl $4, %ecx

- movl %ecx, VAR_SRC

- C

- addl %ebx, %eax C m*(n2+n1) + nadj, low giving carry flag

- leal 1(%edi), %ebx C n2+1

- movl %ebp, %eax C d

- C

- adcl %edx, %ebx C 1 + high(n2<<32 + m*(n2+n1) + nadj) = q1+1

- jz L(q1_ff)

- movl VAR_DST, %ecx

- mull %ebx C (q1+1)*d

- psrlq %mm7, %mm0

- leal -4(%ecx), %ecx

- C

- subl %eax, %esi

- movl VAR_DST_STOP, %eax

- C

- sbbl %edx, %edi C n - (q1+1)*d

- movl %esi, %edi C remainder -> n2

- leal (%ebp,%esi), %edx

- movd %mm0, %esi

- cmovc( %edx, %edi) C n - q1*d if underflow from using q1+1

- sbbl $0, %ebx C q

- cmpl %eax, %ecx

- movl %ebx, (%ecx)

- movl %ecx, VAR_DST

- jne L(integer_top)

-L(integer_loop_done):

-C -----------------------------------------------------------------------------

-C

-C Here, and in integer_one_left below, an sbbl $0 is used rather than a jz

-C q1_ff special case. This make the code a bit smaller and simpler, and

-C costs only 1 cycle (each).

-L(integer_two_left):

- C eax scratch

- C ebx scratch (nadj, q1)

- C ecx scratch (src, dst)

- C edx scratch

- C esi n10

- C edi n2

- C ebp divisor

- C

- C mm7 rshift

- cmpl $0x80000000, %esi C n1 as 0=c, 1=nc

- movl %edi, %eax C n2

- movl PARAM_SRC, %ecx

- leal (%ebp,%esi), %ebx

- cmovc( %esi, %ebx) C nadj = n10 + (-n1 & d), ignoring overflow

- sbbl $-1, %eax C n2+n1

- mull VAR_INVERSE C m*(n2+n1)

- movd (%ecx), %mm0 C src low limb

- movl VAR_DST_STOP, %ecx

- C

- addl %ebx, %eax C m*(n2+n1) + nadj, low giving carry flag

- leal 1(%edi), %ebx C n2+1

- movl %ebp, %eax C d

- adcl %edx, %ebx C 1 + high(n2<<32 + m*(n2+n1) + nadj) = q1+1

- sbbl $0, %ebx

- mull %ebx C (q1+1)*d

- psllq $32, %mm0

- psrlq %mm7, %mm0

- C

- subl %eax, %esi

- C

- sbbl %edx, %edi C n - (q1+1)*d

- movl %esi, %edi C remainder -> n2

- leal (%ebp,%esi), %edx

- movd %mm0, %esi

- cmovc( %edx, %edi) C n - q1*d if underflow from using q1+1

- sbbl $0, %ebx C q

- movl %ebx, -4(%ecx)

-C -----------------------------------------------------------------------------

-L(integer_one_left):

- C eax scratch

- C ebx scratch (nadj, q1)

- C ecx dst

- C edx scratch

- C esi n10

- C edi n2

- C ebp divisor

- C

- C mm7 rshift

- movl VAR_DST_STOP, %ecx

- cmpl $0x80000000, %esi C n1 as 0=c, 1=nc

- movl %edi, %eax C n2

- leal (%ebp,%esi), %ebx

- cmovc( %esi, %ebx) C nadj = n10 + (-n1 & d), ignoring overflow

- sbbl $-1, %eax C n2+n1

- mull VAR_INVERSE C m*(n2+n1)

- C

- addl %ebx, %eax C m*(n2+n1) + nadj, low giving carry flag

- leal 1(%edi), %ebx C n2+1

- movl %ebp, %eax C d

- C

- adcl %edx, %ebx C 1 + high(n2<<32 + m*(n2+n1) + nadj) = q1+1

- sbbl $0, %ebx C q1 if q1+1 overflowed

- mull %ebx

- C

- subl %eax, %esi

- C

- sbbl %edx, %edi C n - (q1+1)*d

- movl %esi, %edi C remainder -> n2

- leal (%ebp,%esi), %edx

- cmovc( %edx, %edi) C n - q1*d if underflow from using q1+1

- sbbl $0, %ebx C q

- movl %ebx, -8(%ecx)

- subl $8, %ecx

-L(integer_none):

- cmpl $0, PARAM_XSIZE

- jne L(fraction_some)

- movl %edi, %eax

-L(fraction_done):

- movl VAR_NORM, %ecx

-L(zero_done):

- movl SAVE_EBP, %ebp

- movl SAVE_EDI, %edi

- movl SAVE_ESI, %esi

- movl SAVE_EBX, %ebx

- addl $STACK_SPACE, %esp

- shrl %cl, %eax

- emms

- ret

-C -----------------------------------------------------------------------------

-C

-C Special case for q1=0xFFFFFFFF, giving q=0xFFFFFFFF meaning the low dword

-C of q*d is simply -d and the remainder n-q*d = n10+d

-L(q1_ff):

- C eax (divisor)

- C ebx (q1+1 == 0)

- C ecx

- C edx

- C esi n10

- C edi n2

- C ebp divisor

- movl VAR_DST, %ecx

- movl VAR_DST_STOP, %edx

- subl $4, %ecx

- psrlq %mm7, %mm0

- leal (%ebp,%esi), %edi C n-q*d remainder -> next n2

- movl %ecx, VAR_DST

- movd %mm0, %esi C next n10

- movl $-1, (%ecx)

- cmpl %ecx, %edx

- jne L(integer_top)

- jmp L(integer_loop_done)

-C -----------------------------------------------------------------------------

-C

-C Being the fractional part, the "source" limbs are all zero, meaning

-C n10=0, n1=0, and hence nadj=0, leading to many instructions eliminated.

-C

-C The loop runs at 15 cycles. The dependent chain is the same as the

-C general case above, but without the n2+n1 stage (due to n1==0), so 15

-C would seem to be the lower bound.

-C

-C A not entirely obvious simplification is that q1+1 never overflows a limb,

-C and so there's no need for the sbbl $0 or jz q1_ff from the general case.

-C q1 is the high word of m*n2+b*n2 and the following shows q1<=b-2 always.

-C rnd() means rounding down to a multiple of d.

-C

-C m*n2 + b*n2 <= m*(d-1) + b*(d-1)

-C = m*d + b*d - m - b

-C = floor((b(b-d)-1)/d)*d + b*d - m - b

-C = rnd(b(b-d)-1) + b*d - m - b

-C = rnd(b(b-d)-1 + b*d) - m - b

-C = rnd(b*b-1) - m - b

-C <= (b-2)*b

-C

-C Unchanged from the general case is that the final quotient limb q can be

-C either q1 or q1+1, and the q1+1 case occurs often. This can be seen from

-C equation 8.4 of the paper which simplifies as follows when n1==0 and

-C n0==0.

-C

-C n-q1*d = (n2*k+q0*d)/b <= d + (d*d-2d)/b

-C

-C As before, the instruction groupings and empty comments show a naive

-C in-order view of the code, which is made a nonsense by out of order

-C execution. There's 17 cycles shown, but it executes at 15.

-C

-C Rotating the store q and remainder->n2 instructions up to the top of the

-C loop gets the run time down from 16 to 15.

- ALIGN(16)

-L(fraction_some):

- C eax

- C ebx

- C ecx

- C edx

- C esi

- C edi carry

- C ebp divisor

- movl PARAM_DST, %esi

- movl VAR_DST_STOP, %ecx C &dst[xsize+2]

- movl %edi, %eax

- subl $8, %ecx C &dst[xsize]

- jmp L(fraction_entry)

- ALIGN(16)

-L(fraction_top):

- C eax n2 carry, then scratch

- C ebx scratch (nadj, q1)

- C ecx dst, decrementing

- C edx scratch

- C esi dst stop point

- C edi (will be n2)

- C ebp divisor

- movl %ebx, (%ecx) C previous q

- movl %eax, %edi C remainder->n2

-L(fraction_entry):

- mull VAR_INVERSE C m*n2

- movl %ebp, %eax C d

- subl $4, %ecx C dst

- leal 1(%edi), %ebx

- C

- addl %edx, %ebx C 1 + high(n2<<32 + m*n2) = q1+1

- mull %ebx C (q1+1)*d

- C

- negl %eax C low of n - (q1+1)*d

- C

- sbbl %edx, %edi C high of n - (q1+1)*d, caring only about carry

- leal (%ebp,%eax), %edx

- cmovc( %edx, %eax) C n - q1*d if underflow from using q1+1

- sbbl $0, %ebx C q

- cmpl %esi, %ecx

- jne L(fraction_top)

- movl %ebx, (%ecx)

- jmp L(fraction_done)

-EPILOGUE()

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