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-rw-r--r--src/gallium/auxiliary/gallivm/lp_bld_arit.c111
1 files changed, 83 insertions, 28 deletions
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
index 816ee70119..7b35dd4bb4 100644
--- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c
+++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c
@@ -1,6 +1,6 @@
/**************************************************************************
*
- * Copyright 2009 VMware, Inc.
+ * Copyright 2009-2010 VMware, Inc.
* All Rights Reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a
@@ -59,6 +59,19 @@
#include "lp_bld_arit.h"
+/*
+ * XXX: Increasing eliminates some artifacts, but adds others, most
+ * noticeably corruption in the Earth halo in Google Earth.
+ */
+#define RCP_NEWTON_STEPS 0
+
+#define RSQRT_NEWTON_STEPS 0
+
+#define EXP_POLY_DEGREE 3
+
+#define LOG_POLY_DEGREE 5
+
+
/**
* Generate min(a, b)
* No checks for special case values of a or b = 1 or 0 are done.
@@ -1248,6 +1261,31 @@ lp_build_sqrt(struct lp_build_context *bld,
}
+/**
+ * Do one Newton-Raphson step to improve reciprocate precision:
+ *
+ * x_{i+1} = x_i * (2 - a * x_i)
+ *
+ * See also:
+ * - http://en.wikipedia.org/wiki/Division_(digital)#Newton.E2.80.93Raphson_division
+ * - http://softwarecommunity.intel.com/articles/eng/1818.htm
+ */
+static INLINE LLVMValueRef
+lp_build_rcp_refine(struct lp_build_context *bld,
+ LLVMValueRef a,
+ LLVMValueRef rcp_a)
+{
+ LLVMValueRef two = lp_build_const_vec(bld->type, 2.0);
+ LLVMValueRef res;
+
+ res = LLVMBuildFMul(bld->builder, a, rcp_a, "");
+ res = LLVMBuildFSub(bld->builder, two, res, "");
+ res = LLVMBuildFMul(bld->builder, rcp_a, res, "");
+
+ return res;
+}
+
+
LLVMValueRef
lp_build_rcp(struct lp_build_context *bld,
LLVMValueRef a)
@@ -1269,32 +1307,16 @@ lp_build_rcp(struct lp_build_context *bld,
return LLVMConstFDiv(bld->one, a);
if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4) {
- /*
- * XXX: Added precision is not always necessary, so only enable this
- * when we have a better system in place to track minimum precision.
- */
-
-#if 1
- /*
- * Do one Newton-Raphson step to improve precision:
- *
- * x1 = (2 - a * rcp(a)) * rcp(a)
- */
-
- LLVMValueRef two = lp_build_const_vec(bld->type, 2.0);
- LLVMValueRef rcp_a;
LLVMValueRef res;
+ unsigned i;
- rcp_a = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", lp_build_vec_type(type), a);
+ res = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", bld->vec_type, a);
- res = LLVMBuildFMul(bld->builder, a, rcp_a, "");
- res = LLVMBuildFSub(bld->builder, two, res, "");
- res = LLVMBuildFMul(bld->builder, res, rcp_a, "");
+ for (i = 0; i < RCP_NEWTON_STEPS; ++i) {
+ res = lp_build_rcp_refine(bld, a, res);
+ }
return res;
-#else
- return lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rcp.ps", lp_build_vec_type(type), a);
-#endif
}
return LLVMBuildFDiv(bld->builder, bld->one, a, "");
@@ -1302,6 +1324,33 @@ lp_build_rcp(struct lp_build_context *bld,
/**
+ * Do one Newton-Raphson step to improve rsqrt precision:
+ *
+ * x_{i+1} = 0.5 * x_i * (3.0 - a * x_i * x_i)
+ *
+ * See also:
+ * - http://softwarecommunity.intel.com/articles/eng/1818.htm
+ */
+static INLINE LLVMValueRef
+lp_build_rsqrt_refine(struct lp_build_context *bld,
+ LLVMValueRef a,
+ LLVMValueRef rsqrt_a)
+{
+ LLVMValueRef half = lp_build_const_vec(bld->type, 0.5);
+ LLVMValueRef three = lp_build_const_vec(bld->type, 3.0);
+ LLVMValueRef res;
+
+ res = LLVMBuildFMul(bld->builder, rsqrt_a, rsqrt_a, "");
+ res = LLVMBuildFMul(bld->builder, a, res, "");
+ res = LLVMBuildFSub(bld->builder, three, res, "");
+ res = LLVMBuildFMul(bld->builder, rsqrt_a, res, "");
+ res = LLVMBuildFMul(bld->builder, half, res, "");
+
+ return res;
+}
+
+
+/**
* Generate 1/sqrt(a)
*/
LLVMValueRef
@@ -1314,8 +1363,18 @@ lp_build_rsqrt(struct lp_build_context *bld,
assert(type.floating);
- if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4)
- return lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rsqrt.ps", lp_build_vec_type(type), a);
+ if(util_cpu_caps.has_sse && type.width == 32 && type.length == 4) {
+ LLVMValueRef res;
+ unsigned i;
+
+ res = lp_build_intrinsic_unary(bld->builder, "llvm.x86.sse.rsqrt.ps", bld->vec_type, a);
+
+ for (i = 0; i < RSQRT_NEWTON_STEPS; ++i) {
+ res = lp_build_rsqrt_refine(bld, a, res);
+ }
+
+ return res;
+ }
return lp_build_rcp(bld, lp_build_sqrt(bld, a));
}
@@ -1821,10 +1880,6 @@ lp_build_log(struct lp_build_context *bld,
}
-#define EXP_POLY_DEGREE 3
-#define LOG_POLY_DEGREE 5
-
-
/**
* Generate polynomial.
* Ex: coeffs[0] + x * coeffs[1] + x^2 * coeffs[2].