shader: read float inline constants on 16-bit operands as half bits (#1582)

The 16-bit encodings of the float inline constants are fixed: the exact
halves of 0.5, 1.0, 2.0 and 4.0 and their negations, and 0x3118 for
1/(2*pi). Read16LaneBits converted the 32-bit value at run time instead,
through PackHalf2x16, which the AMD driver rounds toward zero, so
1/(2*pi) became 0x3117. Use the encodings directly.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Nawid3333
2026-10-17 05:05:40 +02:00
committed by GitHub
parent b95ea4bb5f
commit b6bd9ecae4
@@ -546,9 +546,11 @@ IR::U32 Translator::Read16LaneBits(const Decoder::Operand& operand, bool high_la
auto bits = ReadRawU32(operand);
if (operand.kind == Decoder::OperandKind::FloatInlineConstant) {
// Inline floats encode the operand's width before SDWA or OP_SEL selects bits.
const auto half = IR::F16(ir.Emit(IR::ValueOpcode::ConvertF16F32, {ir.BitCastF32(bits)}));
const auto half_bits = IR::U16(ir.Emit(IR::ValueOpcode::BitCastU16F16, {half}));
bits = IR::U32(ir.Emit(IR::ValueOpcode::ConvertU32U16, {half_bits}));
const auto value = operand.value;
bits = IR::U32(IR::Value(value == 0x3e22f983u
? 0x3118u
: ((value >> 16u) & 0x8000u) |
((((value >> 23u) & 0xffu) - 112u) << 10u)));
}
bits = ApplyBitSourceModifiers(raw_operand, bits);
uint32_t offset = (high_lane ? operand.op_sel_hi : operand.op_sel) ? 16u : 0u;