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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.
#include "sysdeps.h"
// 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
FUNCTION(__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
ENDFUNCTION(__i64_udivmod)
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