diff options
| -rw-r--r-- | src/compiler/glsl/float64.glsl | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/src/compiler/glsl/float64.glsl b/src/compiler/glsl/float64.glsl index e7a7e7860fc..c83e1aa8c97 100644 --- a/src/compiler/glsl/float64.glsl +++ b/src/compiler/glsl/float64.glsl @@ -264,7 +264,25 @@ __fsat64(uint64_t __a) if (__is_nan(__a) || int(a.y) < 0) return 0ul; - if (!__flt64_nonnan(__a, 0x3FF0000000000000ul /* 1.0 */)) + /* IEEE 754 floating point numbers are specifically designed so that, with + * two exceptions, values can be compared by bit-casting to signed integers + * with the same number of bits. + * + * From https://en.wikipedia.org/wiki/IEEE_754-1985#Comparing_floating-point_numbers: + * + * When comparing as 2's-complement integers: If the sign bits differ, + * the negative number precedes the positive number, so 2's complement + * gives the correct result (except that negative zero and positive zero + * should be considered equal). If both values are positive, the 2's + * complement comparison again gives the correct result. Otherwise (two + * negative numbers), the correct FP ordering is the opposite of the 2's + * complement ordering. + * + * We know that both values are not negative, and we know that at least one + * value is not zero. Therefore, we can just use the 2's complement + * comparison ordering. + */ + if (ilt64(0x3FF00000, 0x00000000, a.y, a.x)) return 0x3FF0000000000000ul; return __a; |