tree 6740f3acb5c6ba1013cd36e2cf8737e0ddc75b8c
parent 81fb75a1d75c20d97292cbbe4cde6a1e65871abe
author Rich Felker <dalias@aerifal.cx> 1464041951 -0400
committer Rich Felker <dalias@aerifal.cx> 1464041951 -0400

fix a64l undefined behavior on ILP32 archs, wrong results on LP64 archs

the difference of pointers is a signed type ptrdiff_t; if it is only
32-bit, left-shifting it by 30 bits produces undefined behavior. cast
the difference to an appropriate unsigned type, uint32_t, before
shifting to avoid this.

the a64l function is specified to return a signed 32-bit result in
type long. as noted in the bug report by Ed Schouten, converting
implicitly from uint32_t only produces the desired result when long is
a 32-bit type. since the computation has to be done in unsigned
arithmetic to avoid overflow, simply cast the result to int32_t.

further, POSIX leaves the behavior on invalid input unspecified but
not undefined, so we should not take the difference between the
potentially-null result of strchr and the base pointer without first
checking the result. the simplest behavior is just returning the
partial conversion already performed in this case, so do that.