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draw,llvmpipe: use exponent manipulation instead of exp2 for polygon offset

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Since we explicitly require a integer input we should avoid using exp2 math
(even if we were using optimized versions), which turns the exp2 into a int
sub (plus some casts).

v2: fix bogus uint (needs to be int) math spotted by Matthew, fix comments

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
This commit is contained in:
Roland Scheidegger 2013-11-11 15:11:59 +00:00
parent 2d77e4f922
commit 50f19e3a66
2 changed files with 27 additions and 18 deletions
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19
src/gallium/auxiliary/draw/draw_pipe_offset.c
View file

@ -90,18 +90,23 @@ static void do_offset_tri( struct draw_stage *stage,
float dzdx = fabsf(a * inv_det);
float dzdy = fabsf(b * inv_det);
float zoffset, maxz, bias, mult;
float zoffset, mult;
mult = MAX2(dzdx, dzdy) * offset->scale;
if (stage->draw->floating_point_depth) {
maxz = MAX3(v0[2], v1[2], v2[2]);
float bias;
union fi maxz;
maxz.f = MAX3(v0[2], v1[2], v2[2]);
/* just do the math directly on shifted number */
maxz.ui &= 0xff << 23;
maxz.i -= 23 << 23;
/* Clamping to zero means mrd will be zero for very small numbers,
* but specs do not indicate this should be prevented by clamping
* mrd to smallest normal number instead. */
maxz.i = MAX2(maxz.i, 0);
/**
* XXX: TODO optimize this to quickly resolve a pow2 number through
* an exponent only operation.
*/
bias = offset->units * util_fast_exp2(util_get_float32_exponent(maxz) - 23);
bias = offset->units * maxz.f;
zoffset = bias + mult;
} else {
zoffset = offset->units + mult;

26
src/gallium/drivers/llvmpipe/lp_state_setup.c
View file

@ -31,6 +31,7 @@
#include "util/u_simple_list.h"
#include "os/os_time.h"
#include "gallivm/lp_bld_arit.h"
#include "gallivm/lp_bld_bitarit.h"
#include "gallivm/lp_bld_const.h"
#include "gallivm/lp_bld_debug.h"
#include "gallivm/lp_bld_init.h"
@ -268,8 +269,6 @@ lp_do_offset_tri(struct gallivm_state *gallivm,
LLVMValueRef zeroi = lp_build_const_int32(gallivm, 0);
LLVMValueRef twoi = lp_build_const_int32(gallivm, 2);
LLVMValueRef threei = lp_build_const_int32(gallivm, 3);
LLVMValueRef mantissa_bits, exp, bias;
LLVMValueRef maxz_value, maxz0z1_value;
/* (res12) = cross(e,f).xy */
shuffles[0] = twoi;
@ -319,9 +318,13 @@ lp_do_offset_tri(struct gallivm_state *gallivm,
*
* NOTE: Assumes IEEE float32.
*/
LLVMValueRef c23_shifted, exp_mask, bias, exp;
LLVMValueRef maxz_value, maxz0z1_value;
lp_build_context_init(&int_scalar_bld, gallivm, lp_type_int_vec(32, 32));
mantissa_bits = lp_build_const_int32(gallivm, 23);
c23_shifted = lp_build_const_int32(gallivm, 23 << 23);
exp_mask = lp_build_const_int32(gallivm, 0xff << 23);
maxz0z1_value = lp_build_max(&flt_scalar_bld,
LLVMBuildExtractElement(b, attribv[0], twoi, ""),
@ -331,15 +334,16 @@ lp_do_offset_tri(struct gallivm_state *gallivm,
LLVMBuildExtractElement(b, attribv[2], twoi, ""),
maxz0z1_value);
/**
* XXX: TODO optimize this to quickly resolve a pow2 number through
* an exponent only operation.
*/
exp = lp_build_extract_exponent(&flt_scalar_bld, maxz_value, 0);
exp = lp_build_sub(&int_scalar_bld, exp, mantissa_bits);
exp = lp_build_int_to_float(&flt_scalar_bld, exp);
exp = LLVMBuildBitCast(b, maxz_value, int_scalar_bld.vec_type, "");
exp = lp_build_and(&int_scalar_bld, exp, exp_mask);
exp = lp_build_sub(&int_scalar_bld, exp, c23_shifted);
/* Clamping to zero means mrd will be zero for very small numbers,
* but specs do not indicate this should be prevented by clamping
* mrd to smallest normal number instead. */
exp = lp_build_max(&int_scalar_bld, exp, int_scalar_bld.zero);
exp = LLVMBuildBitCast(b, exp, flt_scalar_bld.vec_type, "");
bias = LLVMBuildFMul(b, lp_build_exp2(&flt_scalar_bld, exp),
bias = LLVMBuildFMul(b, exp,
lp_build_const_float(gallivm, key->pgon_offset_units),
"bias");