glsl: fix atan(0, -1)

Fixes fd.o bug 29388

NOTE: this is a candidate for the 7.8 branch.

diff --git a/src/mesa/slang/library/slang_common_builtin.gc b/src/mesa/slang/library/slang_common_builtin.gc
index d75354deffe71909da2bc2482dfd535d5fff2043..1f5ddbc1ee272a20a34ba0def1c9db461b45167d 100644 (file)
--- a/src/mesa/slang/library/slang_common_builtin.gc
+++ b/src/mesa/slang/library/slang_common_builtin.gc
@@ -411,7 +411,7 @@ float atan(const float y, const float x)
    if (abs(x) > 1.0e-4) {
       r = atan(y / x);
       if (x < 0.0) {
-         r = r + sign(y) * 3.141593;
+         r = r + 3.141593 - 6.283186 * float(y < 0.0);
       }
    }
    else {