diff options
author | José Fonseca <jfonseca@vmware.com> | 2010-10-06 14:06:14 +0100 |
---|---|---|
committer | José Fonseca <jfonseca@vmware.com> | 2010-10-06 18:46:29 +0100 |
commit | 4648846bd6c376877f024ccf300ceac5b0b3dcd6 (patch) | |
tree | 46bab37d4f04b5ff498de00495db0684f7b5338c /src | |
parent | df3505b19341424a605be703a27f50ea585ad71f (diff) |
gallivm: Use a faster (and less accurate) log2 in lod computation.
Diffstat (limited to 'src')
-rw-r--r-- | src/gallium/auxiliary/gallivm/lp_bld_arit.c | 44 | ||||
-rw-r--r-- | src/gallium/auxiliary/gallivm/lp_bld_arit.h | 5 | ||||
-rw-r--r-- | src/gallium/auxiliary/gallivm/lp_bld_sample.c | 4 |
3 files changed, 53 insertions, 0 deletions
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c index 3f9c250ad5..ff94f498ac 100644 --- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c +++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c @@ -2286,3 +2286,47 @@ lp_build_log2(struct lp_build_context *bld, lp_build_log2_approx(bld, x, NULL, NULL, &res); return res; } + + +/** + * Faster (and less accurate) log2. + * + * log2(x) = floor(log2(x)) + frac(x) + * + * See http://www.flipcode.com/archives/Fast_log_Function.shtml + */ +LLVMValueRef +lp_build_fast_log2(struct lp_build_context *bld, + LLVMValueRef x) +{ + const struct lp_type type = bld->type; + LLVMTypeRef vec_type = bld->vec_type; + LLVMTypeRef int_vec_type = bld->int_vec_type; + + unsigned mantissa = lp_mantissa(type); + LLVMValueRef mantmask = lp_build_const_int_vec(type, (1ULL << mantissa) - 1); + LLVMValueRef one = LLVMConstBitCast(bld->one, int_vec_type); + + LLVMValueRef ipart; + LLVMValueRef fpart; + + assert(lp_check_value(bld->type, x)); + + assert(type.floating); + + x = LLVMBuildBitCast(bld->builder, x, int_vec_type, ""); + + /* ipart = floor(log2(x)) - 1 */ + ipart = LLVMBuildLShr(bld->builder, x, lp_build_const_int_vec(type, mantissa), ""); + ipart = LLVMBuildAnd(bld->builder, ipart, lp_build_const_int_vec(type, 255), ""); + ipart = LLVMBuildSub(bld->builder, ipart, lp_build_const_int_vec(type, 128), ""); + ipart = LLVMBuildSIToFP(bld->builder, ipart, vec_type, ""); + + /* fpart = 1.0 + frac(x) */ + fpart = LLVMBuildAnd(bld->builder, x, mantmask, ""); + fpart = LLVMBuildOr(bld->builder, fpart, one, ""); + fpart = LLVMBuildBitCast(bld->builder, fpart, vec_type, ""); + + /* floor(log2(x)) + frac(x) */ + return LLVMBuildFAdd(bld->builder, ipart, fpart, ""); +} diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.h b/src/gallium/auxiliary/gallivm/lp_bld_arit.h index 31efa9921c..3ed4fec233 100644 --- a/src/gallium/auxiliary/gallivm/lp_bld_arit.h +++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.h @@ -212,6 +212,11 @@ LLVMValueRef lp_build_log2(struct lp_build_context *bld, LLVMValueRef a); +LLVMValueRef +lp_build_fast_log2(struct lp_build_context *bld, + LLVMValueRef a); + + void lp_build_exp2_approx(struct lp_build_context *bld, LLVMValueRef x, diff --git a/src/gallium/auxiliary/gallivm/lp_bld_sample.c b/src/gallium/auxiliary/gallivm/lp_bld_sample.c index aee94c1b86..9dee653eee 100644 --- a/src/gallium/auxiliary/gallivm/lp_bld_sample.c +++ b/src/gallium/auxiliary/gallivm/lp_bld_sample.c @@ -243,7 +243,11 @@ lp_build_lod_selector(struct lp_build_sample_context *bld, } /* compute lod = log2(rho) */ +#if 0 lod = lp_build_log2(float_bld, rho); +#else + lod = lp_build_fast_log2(float_bld, rho); +#endif /* add shader lod bias */ if (lod_bias) { |