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mesa: clean-up LOG2() function

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This commit is contained in:
Brian Paul
2012-08-31 08:33:31 -06:00
parent c8a86f717f
commit 36f3f7ebfa
1 changed files with 16 additions and 18 deletions
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src/mesa/main/imports.h
+16 -18
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@@ -164,41 +164,39 @@ static inline int isblank(int ch) { return ch == ' ' || ch == '\t'; }
/***
*** LOG2: Log base 2 of float
***/
#ifdef USE_IEEE
#if 0
/* This is pretty fast, but not accurate enough (only 2 fractional bits).
* Based on code from http://www.stereopsis.com/log2.html
*/
static inline GLfloat LOG2(GLfloat x)
{
#ifdef USE_IEEE
#if 0
/* This is pretty fast, but not accurate enough (only 2 fractional bits).
* Based on code from http://www.stereopsis.com/log2.html
*/
const GLfloat y = x * x * x * x;
const GLuint ix = *((GLuint *) &y);
const GLuint exp = (ix >> 23) & 0xFF;
const GLint log2 = ((GLint) exp) - 127;
return (GLfloat) log2 * (1.0 / 4.0); /* 4, because of x^4 above */
}
#endif
/* Pretty fast, and accurate.
* Based on code from http://www.flipcode.com/totd/
*/
static inline GLfloat LOG2(GLfloat val)
{
/* Pretty fast, and accurate.
* Based on code from http://www.flipcode.com/totd/
*/
fi_type num;
GLint log_2;
num.f = val;
num.f = x;
log_2 = ((num.i >> 23) & 255) - 128;
num.i &= ~(255 << 23);
num.i += 127 << 23;
num.f = ((-1.0f/3) * num.f + 2) * num.f - 2.0f/3;
return num.f + log_2;
}
#else
/*
* NOTE: log_base_2(x) = log(x) / log(2)
* NOTE: 1.442695 = 1/log(2).
*/
#define LOG2(x) ((GLfloat) (log(x) * 1.442695F))
/*
* NOTE: log_base_2(x) = log(x) / log(2)
* NOTE: 1.442695 = 1/log(2).
*/
return (GLfloat) (log(x) * 1.442695F);
#endif
}
/***