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Diffstat (limited to 'runtime/ia32/i64_udivmod.s')
| -rw-r--r-- | runtime/ia32/i64_udivmod.s | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/runtime/ia32/i64_udivmod.s b/runtime/ia32/i64_udivmod.s new file mode 100644 index 0000000..8f1e97d --- /dev/null +++ b/runtime/ia32/i64_udivmod.s @@ -0,0 +1,106 @@ +# ***************************************************************** +# +# The Compcert verified compiler +# +# Xavier Leroy, INRIA Paris-Rocquencourt +# +# Copyright (c) 2013 Institut National de Recherche en Informatique et +# en Automatique. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are met: +# * Redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer. +# * Redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution. +# * Neither the name of the <organization> nor the +# names of its contributors may be used to endorse or promote products +# derived from this software without specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT +# HOLDER> BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, +# EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, +# PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR +# PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF +# LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING +# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS +# SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +# +# ********************************************************************* + +# Helper functions for 64-bit integer arithmetic. IA32 version. + +# Division and remainder + +# Auxiliary function, never called directly from C code +# Input: 20(esp), 24(esp) is dividend N +# 28(esp), 32(esp) is divisor D +# Output: esi:edi is quotient Q +# eax:edx is remainder R +# ebp is preserved + + .text + .globl __i64_udivmod + .balign 16 +__i64_udivmod: + cmpl $0, 32(%esp) # single-word divisor? (DH = 0) + jne 1f + # Special case 64 bits divided by 32 bits + movl 28(%esp), %ecx # divide NH by DL + movl 24(%esp), %eax # (will trap if D = 0) + xorl %edx, %edx + divl %ecx # eax = quotient, edx = remainder + movl %eax, %edi # high word of quotient in edi + movl 20(%esp), %eax # divide rem : NL by DL + divl %ecx # eax = quotient, edx = remainder + movl %eax, %esi # low word of quotient in esi */ + movl %edx, %eax # low word of remainder in eax + xorl %edx, %edx # high word of remainder is 0, in edx + ret + # The general case +1: movl 28(%esp), %ecx # esi:ecx = D + movl 32(%esp), %esi + movl 20(%esp), %eax # edx:eax = N + movl 24(%esp), %edx + # Scale D and N down, giving D' and N', until D' fits in 32 bits +2: shrl $1, %esi # shift D' right by one + rcrl $1, %ecx + shrl $1, %edx # shift N' right by one + rcrl $1, %eax + testl %esi, %esi # repeat until D'H = 0 + jnz 2b + # Divide N' by D' to get an approximate quotient + divl %ecx # eax = quotient, edx = remainder + movl %eax, %esi # save tentative quotient Q in esi + # Check for off by one quotient + # Compute Q * D +3: movl 32(%esp), %ecx + imull %esi, %ecx # ecx = Q * DH + movl 28(%esp), %eax + mull %esi # edx:eax = Q * DL + add %ecx, %edx # edx:eax = Q * D + jc 5f # overflow in addition means Q is too high + # Compare Q * D with N, computing the remainder in the process + movl %eax, %ecx + movl 20(%esp), %eax + subl %ecx, %eax + movl %edx, %ecx + movl 24(%esp), %edx + sbbl %ecx, %edx # edx:eax = N - Q * D + jnc 4f # no carry: N >= Q * D, we are fine + decl %esi # carry: N < Q * D, adjust Q down by 1 + addl 28(%esp), %eax # and remainder up by D + adcl 32(%esp), %edx + # Finished +4: xorl %edi, %edi # high half of quotient is 0 + ret + # Special case when Q * D overflows +5: decl %esi # adjust Q down by 1 + jmp 3b # and redo check & computation of remainder + + .type __i64_udivmod, @function + .size __i64_udivmod, . - __i64_udivmod |