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gallivm: add a version of log2 which handles edge cases

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That means that if input is:
 * - less than zero (to and including -inf) then NaN will be returned
 * - equal to zero (-denorm, -0, +0 or +denorm), then -inf will be returned
 * - +infinity, then +infinity will be returned
 * - NaN, then NaN will be returned
It's a separate function because the checks are a little bit costly
and in most cases are likely unnecessary.

Signed-off-by: Zack Rusin <zackr@vmware.com>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
This commit is contained in:
Zack Rusin 2013-07-16 15:57:11 -04:00
parent 7b672c1503
commit 13e2cd2f2c
3 changed files with 65 additions and 6 deletions
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58
src/gallium/auxiliary/gallivm/lp_bld_arit.c
View file

@ -3349,13 +3349,25 @@ const double lp_build_log2_polynomial[] = {
* See http://www.devmaster.net/forums/showthread.php?p=43580
* http://en.wikipedia.org/wiki/Logarithm#Calculation
* http://www.nezumi.demon.co.uk/consult/logx.htm
*
* If handle_edge_cases is true the function will perform computations
* to match the required D3D10+ behavior for each of the edge cases.
* That means that if input is:
* - less than zero (to and including -inf) then NaN will be returned
* - equal to zero (-denorm, -0, +0 or +denorm), then -inf will be returned
* - +infinity, then +infinity will be returned
* - NaN, then NaN will be returned
*
* Those checks are fairly expensive so if you don't need them make sure
* handle_edge_cases is false.
*/
void
lp_build_log2_approx(struct lp_build_context *bld,
LLVMValueRef x,
LLVMValueRef *p_exp,
LLVMValueRef *p_floor_log2,
LLVMValueRef *p_log2)
LLVMValueRef *p_log2,
boolean handle_edge_cases)
{
LLVMBuilderRef builder = bld->gallivm->builder;
const struct lp_type type = bld->type;
@ -3428,6 +3440,29 @@ lp_build_log2_approx(struct lp_build_context *bld,
logmant = lp_build_mul(bld, y, logmant);
res = lp_build_add(bld, logmant, logexp);
if (type.floating && handle_edge_cases) {
LLVMValueRef negmask, infmask, zmask;
negmask = lp_build_cmp(bld, PIPE_FUNC_LESS, x,
lp_build_const_vec(bld->gallivm, type, 0.0f));
zmask = lp_build_cmp(bld, PIPE_FUNC_EQUAL, x,
lp_build_const_vec(bld->gallivm, type, 0.0f));
infmask = lp_build_cmp(bld, PIPE_FUNC_GEQUAL, x,
lp_build_const_vec(bld->gallivm, type, INFINITY));
/* If x is qual to inf make sure we return inf */
res = lp_build_select(bld, infmask,
lp_build_const_vec(bld->gallivm, type, INFINITY),
res);
/* If x is qual to 0, return -inf */
res = lp_build_select(bld, zmask,
lp_build_const_vec(bld->gallivm, type, -INFINITY),
res);
/* If x is nan or less than 0, return nan */
res = lp_build_select(bld, negmask,
lp_build_const_vec(bld->gallivm, type, NAN),
res);
}
}
if(p_exp) {
@ -3443,12 +3478,31 @@ lp_build_log2_approx(struct lp_build_context *bld,
}
/*
* log2 implementation which doesn't have special code to
* handle edge cases (-inf, 0, inf, NaN). It's faster but
* the results for those cases are undefined.
*/
LLVMValueRef
lp_build_log2(struct lp_build_context *bld,
LLVMValueRef x)
{
LLVMValueRef res;
lp_build_log2_approx(bld, x, NULL, NULL, &res);
lp_build_log2_approx(bld, x, NULL, NULL, &res, FALSE);
return res;
}
/*
* Version of log2 which handles all edge cases.
* Look at documentation of lp_build_log2_approx for
* description of the behavior for each of the edge cases.
*/
LLVMValueRef
lp_build_log2_safe(struct lp_build_context *bld,
LLVMValueRef x)
{
LLVMValueRef res;
lp_build_log2_approx(bld, x, NULL, NULL, &res, TRUE);
return res;
}

7
src/gallium/auxiliary/gallivm/lp_bld_arit.h
View file

@ -308,6 +308,10 @@ LLVMValueRef
lp_build_log2(struct lp_build_context *bld,
LLVMValueRef a);
LLVMValueRef
lp_build_log2_safe(struct lp_build_context *bld,
LLVMValueRef a);
LLVMValueRef
lp_build_fast_log2(struct lp_build_context *bld,
LLVMValueRef a);
@ -328,7 +332,8 @@ lp_build_log2_approx(struct lp_build_context *bld,
LLVMValueRef x,
LLVMValueRef *p_exp,
LLVMValueRef *p_floor_log2,
LLVMValueRef *p_log2);
LLVMValueRef *p_log2,
boolean handle_nans);
LLVMValueRef
lp_build_mod(struct lp_build_context *bld,

6
src/gallium/auxiliary/gallivm/lp_bld_tgsi_action.c
View file

@ -1236,8 +1236,8 @@ lg2_emit_cpu(
struct lp_build_tgsi_context * bld_base,
struct lp_build_emit_data * emit_data)
{
emit_data->output[emit_data->chan] = lp_build_log2(&bld_base->base,
emit_data->args[0]);
emit_data->output[emit_data->chan] = lp_build_log2_safe(&bld_base->base,
emit_data->args[0]);
}
/* TGSI_OPCODE_LOG (CPU Only) */
@ -1253,7 +1253,7 @@ log_emit_cpu(
LLVMValueRef src0 = emit_data->args[0];
lp_build_log2_approx(&bld_base->base, src0,
&p_exp, &p_floor_log2, &p_log2);
&p_exp, &p_floor_log2, &p_log2, FALSE);
emit_data->output[TGSI_CHAN_X] = p_floor_log2;