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GLSL: The LOG2 macro doesn't have enough precision

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It looks like the LOG2 macro only has 8 or 9 bits of precission, but
the ARB_vertex_program spec says "accurate to at least 10 bits".
This commit is contained in:
Ian Romanick
2008-12-18 14:11:06 -08:00
parent 1db6371304
commit 962fa6bbc1
1 changed files with 9 additions and 2 deletions
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src/mesa/shader/prog_execute.c
+9 -2
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@@ -963,7 +963,10 @@ _mesa_execute_program(GLcontext * ctx,
{
GLfloat a[4], result[4];
fetch_vector1(&inst->SrcReg[0], machine, a);
result[0] = result[1] = result[2] = result[3] = LOG2(a[0]);
/* The fast LOG2 macro doesn't meet the precision requirements.
*/
result[0] = result[1] = result[2] = result[3] =
(log(a[0]) * 1.442695F);
store_vector4(inst, machine, result);
}
break;
@@ -1022,7 +1025,11 @@ _mesa_execute_program(GLcontext * ctx,
GLfloat mantissa = FREXPF(t[0], &exponent);
q[0] = (GLfloat) (exponent - 1);
q[1] = (GLfloat) (2.0 * mantissa); /* map [.5, 1) -> [1, 2) */
q[2] = (GLfloat) (q[0] + LOG2(q[1]));
/* The fast LOG2 macro doesn't meet the precision
* requirements.
*/
q[2] = (log(t[0]) * 1.442695F);
}
}
else {