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# *****************************************************************
#
# 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
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