Fix T49253: Cycles blackbody is wrong on AVX2 CPU on Windows

Seems to be bug in optimizer, but managed to reshuffle in a way
which should also give some speedup.

1 files changed, 29 insertions, 24 deletions

diff --git a/intern/cycles/kernel/svm/svm_math_util.h b/intern/cycles/kernel/svm/svm_math_util.h
index 01547b60014..a7f15de7325 100644
--- a/intern/cycles/kernel/svm/svm_math_util.h
+++ b/intern/cycles/kernel/svm/svm_math_util.h
@@ -134,32 +134,37 @@ ccl_device float3 svm_math_blackbody_color(float t) {
 		{  6.72595954e-13f, -2.73059993e-08f,  4.24068546e-04f, -7.52204323e-01f },
 	};
 
-	if(t >= 12000.0f)
+	int i;
+	if(t >= 12000.0f) {
 		return make_float3(0.826270103f, 0.994478524f, 1.56626022f);
+	}
+	else if(t >= 6365.0f) {
+		i = 5;
+	}
+	else if(t >= 3315.0f) {
+		i = 4;
+	}
+	else if(t >= 1902.0f) {
+		i = 3;
+	}
+	else if(t >= 1449.0f) {
+		i = 2;
+	}
+	else if(t >= 1167.0f) {
+		i = 1;
+	}
+	else if(t >= 965.0f) {
+		i = 0;
+	}
+	else {
+		/* For 800 <= t < 965 color does not change in OSL implementation, so keep color the same */
+		return make_float3(4.70366907f, 0.0f, 0.0f);
+	}
 
-	/* Define a macro to reduce stack usage for nvcc */
-#define MAKE_BB_RGB(i) make_float3(\
-		rc[i][0] / t + rc[i][1] * t + rc[i][2],\
-		gc[i][0] / t + gc[i][1] * t + gc[i][2],\
-		((bc[i][0] * t + bc[i][1]) * t + bc[i][2]) * t + bc[i][3])
-
-	if(t >= 6365.0f)
-		return MAKE_BB_RGB(5);
-	if(t >= 3315.0f)
-		return MAKE_BB_RGB(4);
-	if(t >= 1902.0f)
-		return MAKE_BB_RGB(3);
-	if(t >= 1449.0f)
-		return MAKE_BB_RGB(2);
-	if(t >= 1167.0f)
-		return MAKE_BB_RGB(1);
-	if(t >= 965.0f)
-		return MAKE_BB_RGB(0);
-
-#undef MAKE_BB_RGB
-
-	/* For 800 <= t < 965 color does not change in OSL implementation, so keep color the same */
-	return make_float3(4.70366907f, 0.0f, 0.0f);
+	const float t_inv = 1.0f / t;
+	return make_float3(rc[i][0] * t_inv + rc[i][1] * t + rc[i][2],
+	                   gc[i][0] * t_inv + gc[i][1] * t + gc[i][2],
+	                   ((bc[i][0] * t + bc[i][1]) * t + bc[i][2]) * t + bc[i][3]);
 }
 
 ccl_device_inline float3 svm_math_gamma_color(float3 color, float gamma)