IDA 反匯編插件有時會生成 OFSUB 這個宏，它的作用是測試兩個數相減是否溢出，返回溢出標志位。

// ofsub.cpp : 此文件包含 "main" 函數。程序執行將在此處開始并結束。 //#include <iostream> using namespace std;typedef char int8; typedef signed char sint8; typedef unsigned char uint8; typedef short int16; typedef signed short sint16; typedef unsigned short uint16; typedef int int32; typedef signed int sint32; typedef unsigned int uint32; typedef __int64 int64; typedef __int64 sint64; typedef unsigned __int64 uint64;// sign flag template<class T> int8 __SETS__(T x) {if (sizeof(T) == 1)return int8(x) < 0;if (sizeof(T) == 2)return int16(x) < 0;if (sizeof(T) == 4)return int32(x) < 0;return int64(x) < 0; }// overflow flag of subtraction (x-y) template<class T, class U> int8 __OFSUB__(T x, U y) {if (sizeof(T) < sizeof(U)){U x2 = x;int8 sx = __SETS__(x2);return (sx ^ __SETS__(y)) & (sx ^ __SETS__(x2 - y));}else{T y2 = y;int8 sx = __SETS__(x);return (sx ^ __SETS__(y2)) & (sx ^ __SETS__(x - y2));} }int main() {int res;unsigned char c1 = 0x80;unsigned char c2 = 0x01;res = __OFSUB__(c1, c2); // -128 - 1 溢出了cout << res << endl;c1 = 0x7F;c2 = 0x01;res = __OFSUB__(c1, c2); // 127 - 1 沒溢出cout << res << endl; }

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