Postgresql源码中的加法函数：Size add_size(Size s1, Size s2)

甩祸

看到这个函数真是佩服他们的谨慎。一个简单的加法函数，居然写成这样。

/*
* Add two Size values, checking for overflow
*/
Size
add_size(Size s1, Size s2)
{
Sizeresult;
result = s1 + s2;
/* We are assuming Size is an unsigned type here... */
if (result < s1 || result < s2)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("requested shared memory size overflows size_t")));
return result;
}

还考虑了溢出，真够谨慎的。
下面是乘法函数

/*
* Multiply two Size values, checking for overflow
*/
Size
mul_size(Size s1, Size s2)
{
Sizeresult;
if (s1 == 0 || s2 == 0)
return 0;
result = s1 * s2;
/* We are assuming Size is an unsigned type here... */
if (result / s2 != s1)
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("requested shared memory size overflows size_t")));
return result;
}