Signed-off-by: Ilia Mirkin <imir...@alum.mit.edu>
---
Not sure how many steps are needed for the necessary accuracy. Just
doing 2 because that seems like a reasonable number.
.../nouveau/codegen/nv50_ir_lowering_nvc0.cpp | 42 ++++++++++++++++++++--
1 file changed, 39 insertions(+), 3 deletions(-)
diff --git a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
index 87e75e1..9767566 100644
--- a/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
+++ b/src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp
@@ -77,8 +77,9 @@ NVC0LegalizeSSA::handleRCPRSQ(Instruction *i)
bld.setPosition(i, false);
// 1. Take the source and it up.
- Value *src[2], *dst[2], *def = i->getDef(0);
- bld.mkSplit(src, 4, i->getSrc(0));
+ Value *input = i->getSrc(0);
+ Value *src[2], *dst[2], *guess, *def = i->getDef(0);
+ bld.mkSplit(src, 4, input);
// 2. We don't care about the low 32 bits of the destination. Stick a 0 in.
dst[0] = bld.loadImm(NULL, 0);
@@ -93,7 +94,42 @@ NVC0LegalizeSSA::handleRCPRSQ(Instruction *i)
// 4. Recombine the two dst pieces back into the original destination.
bld.setPosition(i, true);
- bld.mkOp2(OP_MERGE, TYPE_U64, def, dst[0], dst[1]);
+ guess = bld.mkOp2v(OP_MERGE, TYPE_U64, bld.getSSA(8), dst[0], dst[1]);
+
+ // 5. Perform 2 Newton-Raphson steps
+ if (i->op == OP_RCP) {
+ // RCP: x_{n+1} = 2 * x_n - input * x_n^2
+ Value *two = bld.getSSA(8);
+
+ bld.mkCvt(OP_CVT, TYPE_F64, two, TYPE_F32, bld.loadImm(NULL, 2.0f));
+
+ guess = bld.mkOp2v(OP_SUB, TYPE_F64, bld.getSSA(8),
+ bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), two,
guess),
+ bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), input,
+ bld.mkOp2v(OP_MUL, TYPE_F64,
bld.getSSA(8), guess, guess)));
+ guess = bld.mkOp2v(OP_SUB, TYPE_F64, bld.getSSA(8),
+ bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), two,
guess),
+ bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), input,
+ bld.mkOp2v(OP_MUL, TYPE_F64,
bld.getSSA(8), guess, guess)));
+ } else {
+ // RSQ: x_{n+1} = x_n (1.5 - 0.5 * input * x_n^2)
+ Value *half_input = bld.getSSA(8), *three_half = bld.getSSA(8);
+ bld.mkCvt(OP_CVT, TYPE_F64, half_input, TYPE_F32, bld.loadImm(NULL,
-0.5f));
+ bld.mkCvt(OP_CVT, TYPE_F64, three_half, TYPE_F32, bld.loadImm(NULL,
1.5f));
+
+ half_input = bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), half_input,
input);
+ // RSQ: x_{n+1} = x_n * (1.5 - 0.5 * input * x_n^2)
+ guess = bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), guess,
+ bld.mkOp3v(OP_MAD, TYPE_F64, bld.getSSA(8),
half_input,
+ bld.mkOp2v(OP_MUL, TYPE_F64,
bld.getSSA(8), guess, guess),
+ three_half));
+ guess = bld.mkOp2v(OP_MUL, TYPE_F64, bld.getSSA(8), guess,
+ bld.mkOp3v(OP_MAD, TYPE_F64, bld.getSSA(8),
half_input,
+ bld.mkOp2v(OP_MUL, TYPE_F64,
bld.getSSA(8), guess, guess),
+ three_half));
+ }
+
+ bld.mkMov(def, guess);
}
bool
--
2.0.5
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