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mesa: Simplify ptn_log() a bit

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Using fdiv lets us drop the fneg. nir_opt_algebraic will re-optimize
this if the driver implements fdiv using fmul and frcp.

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23089>
This commit is contained in:
Alyssa Rosenzweig 2023-07-10 16:05:50 -05:00 • committed by Marge Bot
parent 2198eedd04
commit 5b835f1a08
1 changed files with 2 additions and 3 deletions
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5
src/mesa/program/prog_to_nir.c
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@ -308,7 +308,7 @@ ptn_exp(nir_builder *b, nir_alu_dest dest, nir_ssa_def **src)
/* LOG - Approximate Logarithm Base 2
* dst.x = \lfloor\log_2{|src.x|}\rfloor
* dst.y = |src.x| * 2^{-\lfloor\log_2{|src.x|}\rfloor}}
* dst.y = \frac{|src.x|}{2^{\lfloor\log_2{|src.x|}\rfloor}}
* dst.z = \log_2{|src.x|}
* dst.w = 1.0
*/
@ -321,8 +321,7 @@ ptn_log(nir_builder *b, nir_alu_dest dest, nir_ssa_def **src)
ptn_move_dest_masked(b, dest, floor_log2, WRITEMASK_X);
ptn_move_dest_masked(b, dest,
nir_fmul(b, abs_srcx,
nir_fexp2(b, nir_fneg(b, floor_log2))),
nir_fdiv(b, abs_srcx, nir_fexp2(b, floor_log2)),
WRITEMASK_Y);
ptn_move_dest_masked(b, dest, log2, WRITEMASK_Z);
ptn_move_dest_masked(b, dest, nir_imm_float(b, 1.0), WRITEMASK_W);