diff options
Diffstat (limited to 'src/gallium/auxiliary/gallivm')
| -rw-r--r-- | src/gallium/auxiliary/gallivm/lp_bld_arit.c | 113 | ||||
| -rw-r--r-- | src/gallium/auxiliary/gallivm/lp_bld_arit.h | 10 |
2 files changed, 88 insertions, 35 deletions
diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.c b/src/gallium/auxiliary/gallivm/lp_bld_arit.c index 6ab13506e15..2c049d02934 100644 --- a/src/gallium/auxiliary/gallivm/lp_bld_arit.c +++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.c @@ -2262,6 +2262,71 @@ lp_build_exp2(struct lp_build_context *bld, /** + * Extract the exponent of a IEEE-754 floating point value. + * + * Optionally apply an integer bias. + * + * Result is an integer value with + * + * ifloor(log2(x)) + bias + */ +LLVMValueRef +lp_build_extract_exponent(struct lp_build_context *bld, + LLVMValueRef x, + int bias) +{ + const struct lp_type type = bld->type; + unsigned mantissa = lp_mantissa(type); + LLVMValueRef res; + + assert(type.floating); + + assert(lp_check_value(bld->type, x)); + + x = LLVMBuildBitCast(bld->builder, x, bld->int_vec_type, ""); + + res = LLVMBuildLShr(bld->builder, x, lp_build_const_int_vec(type, mantissa), ""); + res = LLVMBuildAnd(bld->builder, res, lp_build_const_int_vec(type, 255), ""); + res = LLVMBuildSub(bld->builder, res, lp_build_const_int_vec(type, 127 - bias), ""); + + return res; +} + + +/** + * Extract the mantissa of the a floating. + * + * Result is a floating point value with + * + * x / floor(log2(x)) + */ +LLVMValueRef +lp_build_extract_mantissa(struct lp_build_context *bld, + LLVMValueRef x) +{ + const struct lp_type type = bld->type; + unsigned mantissa = lp_mantissa(type); + LLVMValueRef mantmask = lp_build_const_int_vec(type, (1ULL << mantissa) - 1); + LLVMValueRef one = LLVMConstBitCast(bld->one, bld->int_vec_type); + LLVMValueRef res; + + assert(lp_check_value(bld->type, x)); + + assert(type.floating); + + x = LLVMBuildBitCast(bld->builder, x, bld->int_vec_type, ""); + + /* res = x / 2**ipart */ + res = LLVMBuildAnd(bld->builder, x, mantmask, ""); + res = LLVMBuildOr(bld->builder, res, one, ""); + res = LLVMBuildBitCast(bld->builder, res, bld->vec_type, ""); + + return res; +} + + + +/** * Minimax polynomial fit of log2(x)/(x - 1), for x in range [1, 2[ * These coefficients can be generate with * http://www.boost.org/doc/libs/1_36_0/libs/math/doc/sf_and_dist/html/math_toolkit/toolkit/internals2/minimax.html @@ -2385,7 +2450,10 @@ lp_build_log2(struct lp_build_context *bld, /** * Faster (and less accurate) log2. * - * log2(x) = floor(log2(x)) + frac(x) + * log2(x) = floor(log2(x)) - 1 + x / 2**floor(log2(x)) + * + * Piece-wise linear approximation, with exact results when x is a + * power of two. * * See http://www.flipcode.com/archives/Fast_log_Function.shtml */ @@ -2393,35 +2461,21 @@ 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, ""); + assert(bld->type.floating); /* 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, ""); + ipart = lp_build_extract_exponent(bld, x, -1); + ipart = LLVMBuildSIToFP(bld->builder, ipart, bld->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, ""); + /* fpart = x / 2**ipart */ + fpart = lp_build_extract_mantissa(bld, x); - /* floor(log2(x)) + frac(x) */ + /* ipart + fpart */ return LLVMBuildFAdd(bld->builder, ipart, fpart, ""); } @@ -2435,27 +2489,18 @@ LLVMValueRef lp_build_ilog2(struct lp_build_context *bld, LLVMValueRef x) { - const struct lp_type type = bld->type; - LLVMTypeRef int_vec_type = bld->int_vec_type; - - unsigned mantissa = lp_mantissa(type); - LLVMValueRef sqrt2 = lp_build_const_vec(type, 1.4142135623730951); - + LLVMValueRef sqrt2 = lp_build_const_vec(bld->type, M_SQRT2); LLVMValueRef ipart; - assert(lp_check_value(bld->type, x)); + assert(bld->type.floating); - assert(type.floating); + assert(lp_check_value(bld->type, x)); /* x * 2^(0.5) i.e., add 0.5 to the log2(x) */ x = LLVMBuildFMul(bld->builder, x, sqrt2, ""); - x = LLVMBuildBitCast(bld->builder, x, int_vec_type, ""); - /* ipart = floor(log2(x) + 0.5) */ - 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, 127), ""); + ipart = lp_build_extract_exponent(bld, x, 0); return ipart; } diff --git a/src/gallium/auxiliary/gallivm/lp_bld_arit.h b/src/gallium/auxiliary/gallivm/lp_bld_arit.h index 8424384f8f7..c78b61decf0 100644 --- a/src/gallium/auxiliary/gallivm/lp_bld_arit.h +++ b/src/gallium/auxiliary/gallivm/lp_bld_arit.h @@ -215,6 +215,15 @@ lp_build_exp2(struct lp_build_context *bld, LLVMValueRef a); LLVMValueRef +lp_build_extract_exponent(struct lp_build_context *bld, + LLVMValueRef x, + int bias); + +LLVMValueRef +lp_build_extract_mantissa(struct lp_build_context *bld, + LLVMValueRef x); + +LLVMValueRef lp_build_log2(struct lp_build_context *bld, LLVMValueRef a); @@ -226,7 +235,6 @@ LLVMValueRef lp_build_ilog2(struct lp_build_context *bld, LLVMValueRef x); - void lp_build_exp2_approx(struct lp_build_context *bld, LLVMValueRef x, |