Mesa (master): vc4: Apply a Newton-Raphson step to improve RSQ
Eric Anholt
anholt at kemper.freedesktop.org
Sat Oct 18 09:10:27 UTC 2014
Module: Mesa
Branch: master
Commit: 15eb4c59f6504473989e6a064fda11d6c009ed8f
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=15eb4c59f6504473989e6a064fda11d6c009ed8f
Author: Eric Anholt <eric at anholt.net>
Date: Fri Oct 17 15:28:02 2014 +0100
vc4: Apply a Newton-Raphson step to improve RSQ
Fixes all the piglit built-in-functions/*sqrt tests, among others.
---
src/gallium/drivers/vc4/vc4_program.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/src/gallium/drivers/vc4/vc4_program.c b/src/gallium/drivers/vc4/vc4_program.c
index 0046b22..66dff97 100644
--- a/src/gallium/drivers/vc4/vc4_program.c
+++ b/src/gallium/drivers/vc4/vc4_program.c
@@ -313,6 +313,25 @@ tgsi_to_qir_rcp(struct vc4_compile *c,
}
static struct qreg
+tgsi_to_qir_rsq(struct vc4_compile *c,
+ struct tgsi_full_instruction *tgsi_inst,
+ enum qop op, struct qreg *src, int i)
+{
+ struct qreg x = src[0 * 4 + 0];
+ struct qreg r = qir_RSQ(c, x);
+
+ /* Apply a Newton-Raphson step to improve the accuracy. */
+ r = qir_FMUL(c, r, qir_FSUB(c,
+ qir_uniform_f(c, 1.5),
+ qir_FMUL(c,
+ qir_uniform_f(c, 0.5),
+ qir_FMUL(c, x,
+ qir_FMUL(c, r, r)))));
+
+ return r;
+}
+
+static struct qreg
qir_srgb_decode(struct vc4_compile *c, struct qreg srgb)
{
struct qreg low = qir_FMUL(c, srgb, qir_uniform_f(c, 1.0 / 12.92));
@@ -1165,7 +1184,6 @@ emit_tgsi_instruction(struct vc4_compile *c,
[TGSI_OPCODE_IDIV] = { 0, tgsi_to_qir_idiv },
[TGSI_OPCODE_INEG] = { 0, tgsi_to_qir_ineg },
- [TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_alu },
[TGSI_OPCODE_SEQ] = { 0, tgsi_to_qir_seq },
[TGSI_OPCODE_SNE] = { 0, tgsi_to_qir_sne },
[TGSI_OPCODE_SGE] = { 0, tgsi_to_qir_sge },
@@ -1182,7 +1200,7 @@ emit_tgsi_instruction(struct vc4_compile *c,
[TGSI_OPCODE_CMP] = { 0, tgsi_to_qir_cmp },
[TGSI_OPCODE_MAD] = { 0, tgsi_to_qir_mad },
[TGSI_OPCODE_RCP] = { QOP_RCP, tgsi_to_qir_rcp },
- [TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_scalar },
+ [TGSI_OPCODE_RSQ] = { QOP_RSQ, tgsi_to_qir_rsq },
[TGSI_OPCODE_EX2] = { QOP_EXP2, tgsi_to_qir_scalar },
[TGSI_OPCODE_LG2] = { QOP_LOG2, tgsi_to_qir_scalar },
[TGSI_OPCODE_LRP] = { 0, tgsi_to_qir_lrp },
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