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glsl: Use find_msb_uint to implement ir_unop_find_lsb

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(X & -X) calculates a value with only the least significant bit of X
set.  Since there is only one bit set, the LSB is the MSB.

v2: Remove extra int() cast.  Suggested by Matt.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Ian Romanick
2016-07-12 17:40:48 -07:00
parent 5c24750a49
commit 6d5fe1815c
1 changed files with 9 additions and 10 deletions
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19
src/compiler/glsl/ir_constant_expression.cpp
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@@ -1560,16 +1560,15 @@ ir_expression::constant_expression_value(struct hash_table *variable_context)
case ir_unop_find_lsb:
for (unsigned c = 0; c < components; c++) {
if (op[0]->value.i[c] == 0)
data.i[c] = -1;
else {
unsigned pos = 0;
unsigned v = op[0]->value.u[c];
for (; !(v & 1); v >>= 1) {
pos++;
}
data.u[c] = pos;
switch (op[0]->type->base_type) {
case GLSL_TYPE_UINT:
data.i[c] = find_msb_uint(op[0]->value.u[c] & -op[0]->value.u[c]);
break;
case GLSL_TYPE_INT:
data.i[c] = find_msb_uint(op[0]->value.i[c] & -op[0]->value.i[c]);
break;
default:
assert(0);
}
}
break;