Mesa (master): nir/spirv/glsl450: Implement IEEE-compliant handling of atan2(=?UTF-8?Q?=C2=B1=E2=88=9E?=, =?UTF-8?Q?=20=C2=B1=E2=88=9E?=).
Francisco Jerez
currojerez at kemper.freedesktop.org
Tue Jan 31 19:21:01 UTC 2017
Module: Mesa
Branch: master
Commit: 11e9ebbf15ecf49d7ef02c2ec6c2d9d3ff0f1b6e
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=11e9ebbf15ecf49d7ef02c2ec6c2d9d3ff0f1b6e
Author: Francisco Jerez <currojerez at riseup.net>
Date: Mon Jan 23 23:36:46 2017 -0800
nir/spirv/glsl450: Implement IEEE-compliant handling of atan2(±∞, ±∞).
Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
Reviewed-by: Juan A. Suarez Romero <jasuarez at igalia.com>
---
src/compiler/spirv/vtn_glsl450.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/src/compiler/spirv/vtn_glsl450.c b/src/compiler/spirv/vtn_glsl450.c
index 8509f64..dd38cc9 100644
--- a/src/compiler/spirv/vtn_glsl450.c
+++ b/src/compiler/spirv/vtn_glsl450.c
@@ -339,12 +339,32 @@ build_atan2(nir_builder *b, nir_ssa_def *y, nir_ssa_def *x)
nir_ssa_def *rcp_scaled_t = nir_frcp(b, nir_fmul(b, t, scale));
nir_ssa_def *s_over_t = nir_fmul(b, nir_fmul(b, s, scale), rcp_scaled_t);
+ /* For |x| = |y| assume tan = 1 even if infinite (i.e. pretend momentarily
+ * that ∞/∞ = 1) in order to comply with the rather artificial rules
+ * inherited from IEEE 754-2008, namely:
+ *
+ * "atan2(±∞, −∞) is ±3π/4
+ * atan2(±∞, +∞) is ±π/4"
+ *
+ * Note that this is inconsistent with the rules for the neighborhood of
+ * zero that are based on iterated limits:
+ *
+ * "atan2(±0, −0) is ±π
+ * atan2(±0, +0) is ±0"
+ *
+ * but GLSL specifically allows implementations to deviate from IEEE rules
+ * at (0,0), so we take that license (i.e. pretend that 0/0 = 1 here as
+ * well).
+ */
+ nir_ssa_def *tan = nir_bcsel(b, nir_feq(b, nir_fabs(b, x), nir_fabs(b, y)),
+ one, nir_fabs(b, s_over_t));
+
/* Calculate the arctangent and fix up the result if we had flipped the
* coordinate system.
*/
nir_ssa_def *arc = nir_fadd(b, nir_fmul(b, nir_b2f(b, flip),
nir_imm_float(b, M_PI_2f)),
- build_atan(b, nir_fabs(b, s_over_t)));
+ build_atan(b, tan));
/* Rather convoluted calculation of the sign of the result. When x < 0 we
* cannot use fsign because we need to be able to distinguish between
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