thirdparty/scummvm
2
0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

COMMON: Add an optimized intLog2 implementation for gcc using __builtin_clz.

Browse source 
This is done as discussed here:
54f25aa843
This commit is contained in:
Johannes Schickel 2011-07-24 19:54:49 +02:00
parent b609100a56
commit a1bfbe65ba
1 changed files with 15 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

15
common/math.h
View file

@ -50,6 +50,20 @@ struct Complex {
float re, im; float re, im;
}; };
#ifdef __GNUC__
inline int intLog2(uint32 v) {
// This is a slightly optimized implementation of log2 for natural numbers
// targeting gcc. It also saves some binary size over our fallback
// implementation, since it does not need any table.
if (v == 0)
return -1;
else
// This is really "sizeof(unsigned int) * CHAR_BIT - 1" but using 8
// instead of CHAR_BIT is sane enough and it saves us from including
// limits.h
return (sizeof(unsigned int) * 8 - 1) - __builtin_clz(v);
}
#else
// See http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup // See http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup
static const char LogTable256[256] = { static const char LogTable256[256] = {
#define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n #define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n
@ -66,6 +80,7 @@ inline int intLog2(uint32 v) {
else else
return (t = v >> 8) ? 8 + LogTable256[t] : LogTable256[v]; return (t = v >> 8) ? 8 + LogTable256[t] : LogTable256[v];
} }
#endif
inline float rad2deg(float rad) { inline float rad2deg(float rad) {
return rad * 180.0 / M_PI; return rad * 180.0 / M_PI;