diff options
| -rw-r--r-- | src/gallium/auxiliary/gallivm/lp_bld_arit.c | 111 |
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]. |