短整数模数不正确.这真的很奇怪,已经花了我两天的时间.我已经缩小了有问题的代码如下(尽可能简化):
#include <stdio.h>
#include <stdlib.h>
int foo(short Width, short Height, short MSize)
{
short i = 0, k = 0, pos = 0;
short j = 0;
for(j = 1; j < Width - 1; j = j + 1)
{/* a blank loop */}
for(i = 1; i < Height - 1; i = i + 1) {
for(j = 1; j < Width - 1; j = j + 1) {
if((j % MSize) == 0) {
k = k + 1;
}
printf("i=%d, k=%d, j=%d, MSize=%d, j mod MSize=%d\n", (int)i, (int)k, (int)j, (int)MSize, (int)(j % MSize));
if (pos >= 1024) {
fprintf(stderr, "pos = %d, over 1024\n", (int)pos);
}
pos = pos + 1;
}
}
return 0;
}
int main(int argc, char* argv[])
{
foo(32, 32, 8);
return 0;
}
在Debug模式下编译时,上面的代码工作正常,j%MSize的结果是正确的,但是,当在Release模式下编译时,j%MSize的结果总是7,这是无意义的(在Visual Studio 2005下测试/ 2012/2013).没有内存操作,因此不应该由堆栈损坏引起.有人有线索吗？
我看到的输出是(稍加编辑):
j=10, MSize=8, j mod MSize=7
j=11, MSize=8, j mod MSize=7
j=12, MSize=8, j mod MSize=7
j=13, MSize=8, j mod MSize=7
j=14, MSize=8, j mod MSize=7
j=15, MSize=8, j mod MSize=7
j=16, MSize=8, j mod MSize=7
j=17, MSize=8, j mod MSize=7
j=18, MSize=8, j mod MSize=7
j=19, MSize=8, j mod MSize=7
j=20, MSize=8, j mod MSize=7
j=21, MSize=8, j mod MSize=7
j=22, MSize=8, j mod MSize=7
j=23, MSize=8, j mod MSize=7
j=24, MSize=8, j mod MSize=7
j=25, MSize=8, j mod MSize=7
j=26, MSize=8, j mod MSize=7
j=27, MSize=8, j mod MSize=7
以下是构建日志:
1>Project "E:\Code\workspace\C\GeneralC\SNDFeatureExtract\SNDFeatureExtract.vcxproj" on node 2 (Build target(s)).
1>ClCompile:
D:\Program Files\Microsoft Visual Studio 11.0\VC\bin\CL.exe /c /Zi /nologo /W3 /WX- /sdl /O2 /Oi /Oy- /GL /D WIN32 /D NDEBUG /D _CONSOLE /D _MBCS /Gm- /EHsc /MT /GS /Gy /fp:precise /Zc:wchar_t /Zc:forScope /Fo"Release\\" /Fd"Release\vc110.pdb" /Gd /TP /analyze- /errorReport:prompt WeirdBug.cpp
WeirdBug.cpp
Link:
D:\Program Files\Microsoft Visual Studio 11.0\VC\bin\link.exe /ERRORREPORT:PROMPT /OUT:"E:\Code\workspace\C\GeneralC\Release\SNDFeatureExtract.exe" /INCREMENTAL:NO /NOLOGO kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib /MANIFEST /MANIFESTUAC:"level='asInvoker' uiAccess='false'" /manifest:embed /DEBUG /PDB:"E:\Code\workspace\C\GeneralC\Release\SNDFeatureExtract.pdb" /SUBSYSTEM:CONSOLE /OPT:REF /OPT:ICF /LTCG /TLBID:1 /DYNAMICBASE /NXCOMPAT /IMPLIB:"E:\Code\workspace\C\GeneralC\Release\SNDFeatureExtract.lib" /MACHINE:X86 /SAFESEH Release\WeirdBug.obj
Generating code
Finished generating code
SNDFeatureExtract.vcxproj -> E:\Code\workspace\C\GeneralC\Release\SNDFeatureExtract.exe
1>Done Building Project "E:\Code\workspace\C\GeneralC\SNDFeatureExtract\SNDFeatureExtract.vcxproj" (Build target(s)).
以下是VS的反汇编结果:
short i = 0, k = 0, pos = 0;
short j = 0;
for(j = 1; j < Width - 1; j = j + 1)
00801014 mov edi,1FF983C8h
00801019 jl foo+12h (0801012h)
{/* a blank loop */}
for(i = 1; i < Height - 1; i = i + 1) {
0080101B mov edx,1
00801020 mov dword ptr [ebp-4],1
00801027 mov dword ptr [ebp-8],edx
0080102A and ecx,80000007h
00801030 jns foo+37h (0801037h)
00801032 dec ecx
00801033 or ecx,0FFFFFFF8h
00801036 inc ecx
00801037 mov dword ptr [ebp-0Ch],ecx
0080103A lea ebx,[ebx]
00801040 mov eax,1
for(j = 1; j < Width - 1; j = j + 1) {
00801045 mov ebx,eax
if((j % MSize) == 0) {
00801047 test ecx,ecx
00801049 jne foo+4Ch (080104Ch)
k = k + 1;
0080104B inc edi
}
printf_s("i=%d, k=%d, j=%d, MSize=%d, j mod MSize=%d\n", (int)i, (int)k, (int)j, (int)MSize, (int)(j % MSize));
0080104C push ecx
0080104D push 8
0080104F push eax
00801050 movsx eax,di
00801053 push eax
00801054 push edx
00801055 push 80CD30h
0080105A call printf_s (0801266h)
if (pos >= 1024) {
0080105F mov eax,400h
00801064 add esp,18h
00801067 cmp si,ax
0080106A jl foo+86h (0801086h)
fprintf_s(stderr, "pos = %d, over 1024\n", (int)pos);
0080106C movsx eax,si
fprintf_s(stderr, "pos = %d, over 1024\n", (int)pos);
0080106F push eax
00801070 push 80CD5Ch
00801075 call __iob_func (0801175h)
0080107A add eax,40h
0080107D push eax
0080107E call fprintf_s (080127Ch)
00801083 add esp,0Ch
for(j = 1; j < Width - 1; j = j + 1) {
00801086 mov ecx,dword ptr [ebp-0Ch]
00801089 mov edx,dword ptr [ebp-8]
}
pos = pos + 1;
0080108C inc ebx
0080108D movsx eax,bx
00801090 inc esi
00801091 cmp eax,1Fh
00801094 jl foo+47h (0801047h)
{/* a blank loop */}
for(i = 1; i < Height - 1; i = i + 1) {
00801096 mov eax,dword ptr [ebp-4]
00801099 inc eax
0080109A movsx edx,ax
0080109D mov dword ptr [ebp-4],eax
008010A0 mov dword ptr [ebp-8],edx
008010A3 cmp edx,1Fh
008010A6 jl foo+40h (0801040h)
}
}
return 0;
008010A8 pop edi
008010A9 pop esi
008010AA xor eax,eax
008010AC pop ebx
}
008010AD mov esp,ebp
008010AF pop ebp
008010B0 ret
这是因为编译器的优化,这与你的空白循环有关.但我不太清楚问题出在哪里.
要简单地解决问题,请将j声明为:
volatile short j;
它会正常工作.原因程序每次都会从内存而不是寄存器中获取j.
我调试了汇编代码,找出程序计算j%MSize并在空白循环之后将其存储到内存中,并且每次执行printf之前,它只是从内存中获取值而不是重新计算它.
mov ecx,dword ptr [ebp-10h] // j % MSize @ memory
push ecx // j % MSize
mov ecx,dword ptr [ebp-0Ch]
push 8 // MSize
push eax // j
movsx eax,word ptr [IdxY]
movsx esi,di
push esi // k
push eax // IdxY
push ecx // i
// push static string and calling printf
但添加一个易失性,它将表现为:
mov dx,word ptr [j]
movsx eax,dx // j
and eax,80000007h // j % 8
push eax
// push other vars and calling printf
那是重新计算MOD,并将其推入堆栈以进行printf.所以它可能是编译器的错误,因为它应该从内存中获取j,即使没有volatile添加.
由于我现在无法再添加注释:( ..我发现它是/ Oxxx和/ GL标志的错误.它将从下面选择一个:
/O1 /O2 /Ox
它必须选择上述选项之一以及/ GL来查看问题.
我的IDE是Visual Studio 2010 10.0.40219.1 SP1Rel
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