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replace LOG2 with util_fast_log2

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The implementation is somewhat different, although if you go back in
time far enough they're the same, but the one in u_math was changed a
long time back to be faster.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3024>
This commit is contained in:
Dylan Baker 2018-09-06 15:26:19 -07:00
parent f8e4542bad
commit bd4e769515
3 changed files with 3 additions and 33 deletions
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4
src/mesa/swrast/s_span.c
View file

@ -426,7 +426,7 @@ _swrast_compute_lambda(GLfloat dsdx, GLfloat dsdy, GLfloat dtdx, GLfloat dtdy,
GLfloat x = sqrtf(dudx * dudx + dvdx * dvdx);
GLfloat y = sqrtf(dudy * dudy + dvdy * dvdy);
GLfloat rho = MAX2(x, y);
GLfloat lambda = LOG2(rho);
GLfloat lambda = util_fast_log2(rho);
return lambda;
}
@ -453,7 +453,7 @@ _swrast_compute_lambda(GLfloat dsdx, GLfloat dsdy, GLfloat dtdx, GLfloat dtdy,
maxU = MAX2(dsdx2, dsdy2) * texW;
maxV = MAX2(dtdx2, dtdy2) * texH;
rho = MAX2(maxU, maxV);
lambda = LOG2(rho);
lambda = util_fast_log2(rho);
return lambda;
}
#endif

2
src/mesa/swrast/s_texfilter.c
View file

@ -1961,7 +1961,7 @@ sample_lambda_2d_aniso(struct gl_context *ctx,
/* note: we need to have Pmin=sqrt(Pmin2) here, but we can avoid
* this since 0.5*log(x) = log(sqrt(x))
*/
lod = 0.5f * LOG2(Pmin2);
lod = 0.5f * util_fast_log2(Pmin2);
if (adjustLOD) {
/* from swrast/s_texcombine.c _swrast_texture_span */

30
src/util/imports.h
View file

@ -73,36 +73,6 @@ typedef union { float f; int i; unsigned u; } fi_type;
/*@}*/
/***
*** LOG2: Log base 2 of float
***/
static inline float LOG2(float x)
{
#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 float y = x * x * x * x;
const unsigned ix = *((unsigned *) &y);
const unsigned exp = (ix >> 23) & 0xFF;
const int log2 = ((int) exp) - 127;
return (float) 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/
*/
fi_type num;
int log_2;
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;
}
/**
* finite macro.
*/