Module: Mesa
Branch: master
Commit: 013d40d1ceb1c23e8a95c8e4dbbb8cab581be919
URL:
http://cgit.freedesktop.org/mesa/mesa/commit/?id=013d40d1ceb1c23e8a95c8e4dbbb8cab581be919
Author: Francisco Jerez <curroje...@riseup.net>
Date: Tue Jan 24 13:43:07 2017 -0800
glsl: Implement IEEE-compliant handling of atan2(±∞, ±∞).
Reviewed-by: Ian Romanick <ian.d.roman...@intel.com>
Reviewed-by: Juan A. Suarez Romero <jasua...@igalia.com>
---
src/compiler/glsl/builtin_functions.cpp | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/src/compiler/glsl/builtin_functions.cpp
b/src/compiler/glsl/builtin_functions.cpp
index 432df65..b8f9d8f 100644
--- a/src/compiler/glsl/builtin_functions.cpp
+++ b/src/compiler/glsl/builtin_functions.cpp
@@ -3604,11 +3604,31 @@ builtin_builder::_atan2(const glsl_type *type)
body.emit(assign(rcp_scaled_t, rcp(mul(t, scale))));
ir_expression *s_over_t = mul(mul(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).
+ */
+ ir_expression *tan = csel(equal(abs(x), abs(y)),
+ imm(1.0f, n), abs(s_over_t));
+
/* Calculate the arctangent and fix up the result if we had flipped the
* coordinate system.
*/
ir_variable *arc = body.make_temp(type, "arc");
- do_atan(body, type, arc, abs(s_over_t));
+ do_atan(body, type, arc, tan);
body.emit(assign(arc, add(arc, mul(b2f(flip), imm(M_PI_2f)))));
/* Rather convoluted calculation of the sign of the result. When x < 0 we
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