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authorManfred Ernst <[email protected]>2013-06-12 20:03:02 -0700
committerStéphane Marchesin <[email protected]>2013-06-12 20:24:48 -0700
commitbf2c074a2fb122bafbbe0f3c7978b89685f2698b (patch)
treea6be04e9ebc0ec3fbdc71697d7d9c3af4dfd5830 /src/gallium/auxiliary/util
parent3475b2213381cdbda7a620d4c0c7708f6969f489 (diff)
mesa: Fix bug in unclamped float to ubyte conversion.
Problem: The IEEE float optimized version of UNCLAMPED_FLOAT_TO_UBYTE in macros.h computed incorrect results for inputs in the range 0x3f7f0000 (=0.99609375) to 0x3f7f7f80 (=0.99803924560546875) inclusive. 0x3f7f7f80 is the IEEE float value that results in 254.5 when multiplied by 255. With rounding mode "round to closest even integer", this is the largest float in the range 0.0-1.0 that is converted to 254 by the generic implementation of UNCLAMPED_FLOAT_TO_UBYTE. The IEEE float optimized version incorrectly defined the cut-off for mapping to 255 as 0x3f7f0000 (=255.0/256.0). The same bug was present in the function float_to_ubyte in u_math.h. Fix: The proposed fix replaces the incorrect cut-off value by 0x3f800000, which is the IEEE float representation of 1.0f. 0x3f7f7f81 (or any value in between) would also work, but 1.0f is probably cleaner. The patch does not regress piglit on llvmpipe and on i965 on sandy bridge. Tested-by Stéphane Marchesin <[email protected]> Reviewed-by Stéphane Marchesin <[email protected]> Reviewed-by: Brian Paul <[email protected]>
Diffstat (limited to 'src/gallium/auxiliary/util')
-rw-r--r--src/gallium/auxiliary/util/u_math.h3
1 files changed, 1 insertions, 2 deletions
diff --git a/src/gallium/auxiliary/util/u_math.h b/src/gallium/auxiliary/util/u_math.h
index 607fbecb02f..64d16cbe715 100644
--- a/src/gallium/auxiliary/util/u_math.h
+++ b/src/gallium/auxiliary/util/u_math.h
@@ -540,14 +540,13 @@ ubyte_to_float(ubyte ub)
static INLINE ubyte
float_to_ubyte(float f)
{
- const int ieee_0996 = 0x3f7f0000; /* 0.996 or so */
union fi tmp;
tmp.f = f;
if (tmp.i < 0) {
return (ubyte) 0;
}
- else if (tmp.i >= ieee_0996) {
+ else if (tmp.i >= 0x3f800000 /* 1.0f */) {
return (ubyte) 255;
}
else {