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glsl: Extract ir_unop_find_msb implementation to a separate function

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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 17:39:26 -07:00
parent d75034b3a2
commit 5c24750a49
1 changed files with 34 additions and 15 deletions
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49
src/compiler/glsl/ir_constant_expression.cpp
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@@ -494,6 +494,31 @@ bitfield_reverse(uint32_t v)
return r;
}
static int
find_msb_uint(uint32_t v)
{
int count = 0;
/* If v == 0, then the loop will terminate when count == 32. In that case
* 31-count will produce the -1 result required by GLSL findMSB().
*/
while (((v & (1u << 31)) == 0) && count != 32) {
count++;
v <<= 1;
}
return 31 - count;
}
static int
find_msb_int(int32_t v)
{
/* If v is signed, findMSB() returns the position of the most significant
* zero bit.
*/
return find_msb_uint(v < 0 ? ~v : v);
}
ir_constant *
ir_expression::constant_expression_value(struct hash_table *variable_context)
{
@@ -1520,21 +1545,15 @@ ir_expression::constant_expression_value(struct hash_table *variable_context)
case ir_unop_find_msb:
for (unsigned c = 0; c < components; c++) {
int v = op[0]->value.i[c];
if (v == 0 || (op[0]->type->base_type == GLSL_TYPE_INT && v == -1))
data.i[c] = -1;
else {
int count = 0;
unsigned top_bit = op[0]->type->base_type == GLSL_TYPE_UINT
? 0 : v & (1u << 31);
while (((v & (1u << 31)) == top_bit) && count != 32) {
count++;
v <<= 1;
}
data.i[c] = 31 - count;
switch (op[0]->type->base_type) {
case GLSL_TYPE_UINT:
data.i[c] = find_msb_uint(op[0]->value.u[c]);
break;
case GLSL_TYPE_INT:
data.i[c] = find_msb_int(op[0]->value.i[c]);
break;
default:
assert(0);
}
}
break;