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glsl: Add constant evaluation of bit built-ins.

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v2: Order bits from LSB end (31 - count) for ir_unop_find_msb.
v3: Add ir_triop_bitfield_extract as an exception to the op[0]->type ==
    op[1]->type assertion in ir_constant_expression.cpp.

Reviewed-by: Chris Forbes <chrisf@ijw.co.nz> [v2]
This commit is contained in:
Matt Turner
2013-04-21 12:33:59 -07:00
parent 499d8c6545
commit 9c04b8c28c
1 changed files with 125 additions and 1 deletions
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126
src/glsl/ir_constant_expression.cpp
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@@ -393,7 +393,8 @@ ir_expression::constant_expression_value(struct hash_table *variable_context)
if (op[1] != NULL)
assert(op[0]->type->base_type == op[1]->type->base_type ||
this->operation == ir_binop_lshift ||
this->operation == ir_binop_rshift);
this->operation == ir_binop_rshift ||
this->operation == ir_triop_bitfield_extract);
bool op0_scalar = op[0]->type->is_scalar();
bool op1_scalar = op[1] != NULL && op[1]->type->is_scalar();
@@ -1248,6 +1249,102 @@ ir_expression::constant_expression_value(struct hash_table *variable_context)
}
break;
case ir_unop_bitfield_reverse:
/* http://graphics.stanford.edu/~seander/bithacks.html#BitReverseObvious */
for (unsigned c = 0; c < components; c++) {
unsigned int v = op[0]->value.u[c]; // input bits to be reversed
unsigned int r = v; // r will be reversed bits of v; first get LSB of v
int s = sizeof(v) * CHAR_BIT - 1; // extra shift needed at end
for (v >>= 1; v; v >>= 1) {
r <<= 1;
r |= v & 1;
s--;
}
r <<= s; // shift when v's highest bits are zero
data.u[c] = r;
}
break;
case ir_unop_bit_count:
for (unsigned c = 0; c < components; c++) {
unsigned count = 0;
unsigned v = op[0]->value.u[c];
for (; v; count++) {
v &= v - 1;
}
data.u[c] = count;
}
break;
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;
int top_bit = op[0]->type->base_type == GLSL_TYPE_UINT
? 0 : v & (1 << 31);
while (((v & (1 << 31)) == top_bit) && count != 32) {
count++;
v <<= 1;
}
data.i[c] = 31 - count;
}
}
break;
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;
}
}
break;
case ir_triop_bitfield_extract: {
int offset = op[1]->value.i[0];
int bits = op[2]->value.i[0];
for (unsigned c = 0; c < components; c++) {
if (bits == 0)
data.u[c] = 0;
else if (offset < 0 || bits < 0)
data.u[c] = 0; /* Undefined, per spec. */
else if (offset + bits > 32)
data.u[c] = 0; /* Undefined, per spec. */
else {
if (op[0]->type->base_type == GLSL_TYPE_INT) {
/* int so that the right shift will sign-extend. */
int value = op[0]->value.i[c];
value <<= 32 - bits - offset;
value >>= 32 - bits;
data.i[c] = value;
} else {
unsigned value = op[0]->value.u[c];
value <<= 32 - bits - offset;
value >>= 32 - bits;
data.u[c] = value;
}
}
}
break;
}
case ir_triop_lrp: {
assert(op[0]->type->base_type == GLSL_TYPE_FLOAT);
assert(op[1]->type->base_type == GLSL_TYPE_FLOAT);
@@ -1261,6 +1358,33 @@ ir_expression::constant_expression_value(struct hash_table *variable_context)
break;
}
case ir_quadop_bitfield_insert: {
int offset = op[2]->value.i[0];
int bits = op[3]->value.i[0];
for (unsigned c = 0; c < components; c++) {
if (bits == 0)
data.u[c] = op[0]->value.u[c];
else if (offset < 0 || bits < 0)
data.u[c] = 0; /* Undefined, per spec. */
else if (offset + bits > 32)
data.u[c] = 0; /* Undefined, per spec. */
else {
unsigned insert_mask = ((1 << bits) - 1) << offset;
unsigned insert = op[1]->value.u[c];
insert <<= offset;
insert &= insert_mask;
unsigned base = op[0]->value.u[c];
base &= ~insert_mask;
data.u[c] = base | insert;
}
}
break;
}
case ir_quadop_vector:
for (unsigned c = 0; c < this->type->vector_elements; c++) {
switch (this->type->base_type) {