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Diffstat (limited to 'runtime/ia32/i64_udivmod.S')
| -rw-r--r-- | runtime/ia32/i64_udivmod.S | 104 |
1 files changed, 104 insertions, 0 deletions
diff --git a/runtime/ia32/i64_udivmod.S b/runtime/ia32/i64_udivmod.S new file mode 100644 index 0000000..dccfc28 --- /dev/null +++ b/runtime/ia32/i64_udivmod.S @@ -0,0 +1,104 @@ +// ***************************************************************** +// +// 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) |