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nir/spirv/glsl450: Implement IEEE-compliant handling of atan2(±∞, ±∞).

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Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Juan A. Suarez Romero <jasuarez@igalia.com>
This commit is contained in:
Francisco Jerez
2017-01-23 23:36:46 -08:00
parent 013d40d1ce
commit 11e9ebbf15
1 changed files with 21 additions and 1 deletions
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22
src/compiler/spirv/vtn_glsl450.c
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@@ -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