Mesa (master): pan/bi: Lower frcp to Newton-Raphson

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Module: Mesa
Branch: master
Commit: c5e5d11599f998dc89ad192fc85feb3c14b4e97a
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=c5e5d11599f998dc89ad192fc85feb3c14b4e97a

Author: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Date:   Fri Jan 15 15:38:35 2021 -0500

pan/bi: Lower frcp to Newton-Raphson

For G71 but should work on any Bifrost, probably overlaps some CL stuff.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Acked-by: Boris Brezillon <boris.brezillon at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8894>

---

 src/panfrost/bifrost/bifrost_compile.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/panfrost/bifrost/bifrost_compile.c b/src/panfrost/bifrost/bifrost_compile.c
index 927a33d34ad..f73c74b9467 100644
--- a/src/panfrost/bifrost/bifrost_compile.c
+++ b/src/panfrost/bifrost/bifrost_compile.c
@@ -974,6 +974,21 @@ bi_fmul_f32(bi_builder *b, bi_index s0, bi_index s1)
         return bi_fma_f32(b, s0, s1, bi_imm_f32(-0.0f), BI_ROUND_NONE);
 }
 
+/* Approximate with FRCP_APPROX.f32 and apply a single iteration of
+ * Newton-Raphson to improve precision */
+
+static void
+bi_lower_frcp_32(bi_builder *b, bi_index dst, bi_index s0)
+{
+        bi_index x1 = bi_frcp_approx_f32(b, s0);
+        bi_index m  = bi_frexpm_f32(b, s0, false, false);
+        bi_index e  = bi_frexpe_f32(b, bi_neg(s0), false, false);
+        bi_index t1 = bi_fma_rscale_f32(b, m, bi_neg(x1), bi_imm_f32(1.0),
+                        bi_zero(), BI_ROUND_NONE, BI_SPECIAL_N);
+        bi_fma_rscale_f32_to(b, dst, t1, x1, x1, e,
+                        BI_ROUND_NONE, BI_SPECIAL_NONE);
+}
+
 static void
 bi_emit_alu(bi_builder *b, nir_alu_instr *instr)
 {