KonstantinSeurer
/
mesa
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

gallivm: Less code duplication in log computation.

This commit is contained in:
José Fonseca 2010-10-09 12:11:20 +01:00
parent 52427f0ba7
commit 81a09c8a97
2 changed files with 88 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

113
src/gallium/auxiliary/gallivm/lp_bld_arit.c
View File

@ -2261,6 +2261,71 @@ 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
@ -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;
}

10
src/gallium/auxiliary/gallivm/lp_bld_arit.h
View File

@ -214,6 +214,15 @@ LLVMValueRef
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,