367 lines
15 KiB
C
367 lines
15 KiB
C
/**************************************************************************
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*
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* Copyright 2013 VMware, Inc.
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* All Rights Reserved.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sub license, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice (including the
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* next paragraph) shall be included in all copies or substantial portions
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* of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.
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* IN NO EVENT SHALL VMWARE AND/OR ITS SUPPLIERS BE LIABLE FOR
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* ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*
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**************************************************************************/
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/**
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* @file
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* Format conversion code for srgb formats.
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*
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* Functions for converting from srgb to linear and vice versa.
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* From http://www.opengl.org/registry/specs/EXT/texture_sRGB.txt:
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*
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* srgb->linear:
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* cl = cs / 12.92, cs <= 0.04045
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* cl = ((cs + 0.055)/1.055)^2.4, cs > 0.04045
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*
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* linear->srgb:
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* if (isnan(cl)) {
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* Map IEEE-754 Not-a-number to zero.
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* cs = 0.0;
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* } else if (cl > 1.0) {
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* cs = 1.0;
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* } else if (cl < 0.0) {
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* cs = 0.0;
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* } else if (cl < 0.0031308) {
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* cs = 12.92 * cl;
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* } else {
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* cs = 1.055 * pow(cl, 0.41666) - 0.055;
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* }
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*
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* This does not need to be accurate, however at least for d3d10
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* (http://msdn.microsoft.com/en-us/library/windows/desktop/dd607323%28v=vs.85%29.aspx):
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* 1) For srgb->linear, it is required that the error on the srgb side is
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* not larger than 0.5f, which I interpret that if you map the value back
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* to srgb from linear using the ideal conversion, it would not be off by
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* more than 0.5f (that is, it would map to the same 8-bit integer value
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* as it was before conversion to linear).
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* 2) linear->srgb is permitted 0.6f which luckily looks like quite a large
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* error is allowed.
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* 3) Additionally, all srgb values converted to linear and back must result
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* in the same value as they were originally.
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*
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* @author Roland Scheidegger <sroland@vmware.com>
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*/
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#include "util/u_debug.h"
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#include "util/u_math.h"
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#include "lp_bld_type.h"
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#include "lp_bld_const.h"
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#include "lp_bld_arit.h"
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#include "lp_bld_bitarit.h"
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#include "lp_bld_logic.h"
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#include "lp_bld_format.h"
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/**
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* Convert srgb int values to linear float values.
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* Several possibilities how to do this, e.g.
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* - table
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* - doing the pow() with int-to-float and float-to-int tricks
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* (http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent)
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* - just using standard polynomial approximation
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* (3rd order polynomial is required for crappy but just sufficient accuracy)
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*
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* @param src integer (vector) value(s) to convert
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* (chan_bits bit values unpacked to 32 bit already).
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*/
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LLVMValueRef
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lp_build_srgb_to_linear(struct gallivm_state *gallivm,
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struct lp_type src_type,
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unsigned chan_bits,
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LLVMValueRef src)
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{
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struct lp_type f32_type = lp_type_float_vec(32, src_type.length * 32);
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struct lp_build_context f32_bld;
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LLVMValueRef srcf, part_lin, part_pow, is_linear, lin_const, lin_thresh;
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double coeffs[4] = {0.0023f,
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0.0030f / 255.0f,
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0.6935f / (255.0f * 255.0f),
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0.3012f / (255.0f * 255.0f * 255.0f)
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};
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assert(src_type.width == 32);
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/* Technically this would work with more bits too but would be inaccurate. */
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assert(chan_bits <= 8);
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lp_build_context_init(&f32_bld, gallivm, f32_type);
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/*
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* using polynomial: (src * (src * (src * 0.3012 + 0.6935) + 0.0030) + 0.0023)
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* ( poly = 0.3012*x^3 + 0.6935*x^2 + 0.0030*x + 0.0023)
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* (found with octave polyfit and some magic as I couldn't get the error
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* function right). Using the above mentioned error function, the values stay
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* within +-0.35, except for the lowest values - hence tweaking linear segment
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* to cover the first 16 instead of the first 11 values (the error stays
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* just about acceptable there too).
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* Hence: lin = src > 15 ? poly : src / 12.6
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* This function really only makes sense for vectors, should use LUT otherwise.
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* All in all (including float conversion) 11 instructions (with sse4.1),
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* 6 constants (polynomial could be done with 1 instruction less at the cost
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* of slightly worse dependency chain, fma should also help).
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*/
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/* doing the 1/255 mul as part of the approximation */
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srcf = lp_build_int_to_float(&f32_bld, src);
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if (chan_bits != 8) {
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/* could adjust all the constants instead */
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LLVMValueRef rescale_const = lp_build_const_vec(gallivm, f32_type,
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255.0f / ((1 << chan_bits) - 1));
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srcf = lp_build_mul(&f32_bld, srcf, rescale_const);
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}
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lin_const = lp_build_const_vec(gallivm, f32_type, 1.0f / (12.6f * 255.0f));
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part_lin = lp_build_mul(&f32_bld, srcf, lin_const);
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part_pow = lp_build_polynomial(&f32_bld, srcf, coeffs, 4);
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lin_thresh = lp_build_const_vec(gallivm, f32_type, 15.0f);
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is_linear = lp_build_compare(gallivm, f32_type, PIPE_FUNC_LEQUAL, srcf, lin_thresh);
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return lp_build_select(&f32_bld, is_linear, part_lin, part_pow);
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}
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/**
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* Convert linear float values to srgb int values.
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* Several possibilities how to do this, e.g.
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* - use table (based on exponent/highest order mantissa bits) and do
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* linear interpolation (https://gist.github.com/rygorous/2203834)
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* - Chebyshev polynomial
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* - Approximation using reciprocals
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* - using int-to-float and float-to-int tricks for pow()
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* (http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent)
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*
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* @param src float (vector) value(s) to convert.
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*/
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static LLVMValueRef
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lp_build_linear_to_srgb(struct gallivm_state *gallivm,
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struct lp_type src_type,
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unsigned chan_bits,
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LLVMValueRef src)
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{
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LLVMBuilderRef builder = gallivm->builder;
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struct lp_build_context f32_bld;
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LLVMValueRef lin_thresh, lin, lin_const, is_linear, tmp, pow_final;
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lp_build_context_init(&f32_bld, gallivm, src_type);
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src = lp_build_clamp(&f32_bld, src, f32_bld.zero, f32_bld.one);
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if (0) {
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/*
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* using int-to-float and float-to-int trick for pow().
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* This is much more accurate than necessary thanks to the correction,
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* but it most certainly makes no sense without rsqrt available.
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* Bonus points if you understand how this works...
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* All in all (including min/max clamp, conversion) 19 instructions.
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*/
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float exp_f = 2.0f / 3.0f;
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/* some compilers can't do exp2f, so this is exp2f(127.0f/exp_f - 127.0f) */
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float exp2f_c = 1.30438178253e+19f;
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float coeff_f = 0.62996f;
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LLVMValueRef pow_approx, coeff, x2, exponent, pow_1, pow_2;
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struct lp_type int_type = lp_int_type(src_type);
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/*
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* First calculate approx x^8/12
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*/
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exponent = lp_build_const_vec(gallivm, src_type, exp_f);
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coeff = lp_build_const_vec(gallivm, src_type,
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exp2f_c * powf(coeff_f, 1.0f / exp_f));
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/* premultiply src */
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tmp = lp_build_mul(&f32_bld, coeff, src);
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/* "log2" */
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tmp = LLVMBuildBitCast(builder, tmp, lp_build_vec_type(gallivm, int_type), "");
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tmp = lp_build_int_to_float(&f32_bld, tmp);
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/* multiply for pow */
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tmp = lp_build_mul(&f32_bld, tmp, exponent);
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/* "exp2" */
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pow_approx = lp_build_itrunc(&f32_bld, tmp);
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pow_approx = LLVMBuildBitCast(builder, pow_approx,
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lp_build_vec_type(gallivm, src_type), "");
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/*
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* Since that pow was inaccurate (like 3 bits, though each sqrt step would
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* give another bit), compensate the error (which is why we chose another
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* exponent in the first place).
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*/
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/* x * x^(8/12) = x^(20/12) */
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pow_1 = lp_build_mul(&f32_bld, pow_approx, src);
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/* x * x * x^(-4/12) = x^(20/12) */
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/* Should avoid using rsqrt if it's not available, but
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* using x * x^(4/12) * x^(4/12) instead will change error weight */
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tmp = lp_build_fast_rsqrt(&f32_bld, pow_approx);
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x2 = lp_build_mul(&f32_bld, src, src);
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pow_2 = lp_build_mul(&f32_bld, x2, tmp);
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/* average the values so the errors cancel out, compensate bias,
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* we also squeeze the 1.055 mul of the srgb conversion plus the 255.0 mul
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* for conversion to int in here */
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tmp = lp_build_add(&f32_bld, pow_1, pow_2);
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coeff = lp_build_const_vec(gallivm, src_type,
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1.0f / (3.0f * coeff_f) * 0.999852f *
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powf(1.055f * 255.0f, 4.0f));
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pow_final = lp_build_mul(&f32_bld, tmp, coeff);
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/* x^(5/12) = rsqrt(rsqrt(x^20/12)) */
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if (lp_build_fast_rsqrt_available(src_type)) {
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pow_final = lp_build_fast_rsqrt(&f32_bld,
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lp_build_fast_rsqrt(&f32_bld, pow_final));
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}
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else {
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pow_final = lp_build_sqrt(&f32_bld, lp_build_sqrt(&f32_bld, pow_final));
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}
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pow_final = lp_build_add(&f32_bld, pow_final,
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lp_build_const_vec(gallivm, src_type, -0.055f * 255.0f));
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}
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else {
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/*
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* using "rational polynomial" approximation here.
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* Essentially y = a*x^0.375 + b*x^0.5 + c, with also
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* factoring in the 255.0 mul and the scaling mul.
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* (a is closer to actual value so has higher weight than b.)
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* Note: the constants are magic values. They were found empirically,
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* possibly could be improved but good enough (be VERY careful with
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* error metric if you'd want to tweak them, they also MUST fit with
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* the crappy polynomial above for srgb->linear since it is required
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* that each srgb value maps back to the same value).
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* This function has an error of max +-0.17. Not sure this is actually
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* enough, we require +-0.6 but that may include the +-0.5 from integer
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* conversion. Seems to pass all relevant tests though...
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* For the approximated srgb->linear values the error is naturally larger
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* (+-0.42) but still accurate enough (required +-0.5 essentially).
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* All in all (including min/max clamp, conversion) 15 instructions.
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* FMA would help (minus 2 instructions).
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*/
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LLVMValueRef x05, x0375, a_const, b_const, c_const, tmp2;
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if (lp_build_fast_rsqrt_available(src_type)) {
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tmp = lp_build_fast_rsqrt(&f32_bld, src);
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x05 = lp_build_mul(&f32_bld, src, tmp);
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}
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else {
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/*
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* I don't really expect this to be practical without rsqrt
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* but there's no reason for triple punishment so at least
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* save the otherwise resulting division and unnecessary mul...
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*/
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x05 = lp_build_sqrt(&f32_bld, src);
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}
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tmp = lp_build_mul(&f32_bld, x05, src);
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if (lp_build_fast_rsqrt_available(src_type)) {
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x0375 = lp_build_fast_rsqrt(&f32_bld, lp_build_fast_rsqrt(&f32_bld, tmp));
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}
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else {
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x0375 = lp_build_sqrt(&f32_bld, lp_build_sqrt(&f32_bld, tmp));
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}
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a_const = lp_build_const_vec(gallivm, src_type, 0.675f * 1.0622 * 255.0f);
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b_const = lp_build_const_vec(gallivm, src_type, 0.325f * 1.0622 * 255.0f);
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c_const = lp_build_const_vec(gallivm, src_type, -0.0620f * 255.0f);
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tmp = lp_build_mul(&f32_bld, a_const, x0375);
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tmp2 = lp_build_mad(&f32_bld, b_const, x05, c_const);
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pow_final = lp_build_add(&f32_bld, tmp, tmp2);
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}
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/* linear part is easy */
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lin_const = lp_build_const_vec(gallivm, src_type, 12.92f * 255.0f);
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lin = lp_build_mul(&f32_bld, src, lin_const);
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lin_thresh = lp_build_const_vec(gallivm, src_type, 0.0031308f);
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is_linear = lp_build_compare(gallivm, src_type, PIPE_FUNC_LEQUAL, src, lin_thresh);
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tmp = lp_build_select(&f32_bld, is_linear, lin, pow_final);
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if (chan_bits != 8) {
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/* could adjust all the constants instead */
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LLVMValueRef rescale_const = lp_build_const_vec(gallivm, src_type,
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((1 << chan_bits) - 1) / 255.0f);
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tmp = lp_build_mul(&f32_bld, tmp, rescale_const);
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}
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f32_bld.type.sign = 0;
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return lp_build_iround(&f32_bld, tmp);
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}
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/**
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* Convert linear float soa values to packed srgb AoS values.
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* This only handles packed formats which are 4x8bit in size
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* (rgba and rgbx plus swizzles), and 16bit 565-style formats
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* with no alpha. (In the latter case the return values won't be
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* fully packed, it will look like r5g6b5x16r5g6b5x16...)
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*
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* @param src float SoA (vector) values to convert.
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*/
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LLVMValueRef
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lp_build_float_to_srgb_packed(struct gallivm_state *gallivm,
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const struct util_format_description *dst_fmt,
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struct lp_type src_type,
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LLVMValueRef *src)
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{
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LLVMBuilderRef builder = gallivm->builder;
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unsigned chan;
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struct lp_build_context f32_bld;
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struct lp_type int32_type = lp_int_type(src_type);
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LLVMValueRef tmpsrgb[4], alpha, dst;
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lp_build_context_init(&f32_bld, gallivm, src_type);
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/* rgb is subject to linear->srgb conversion, alpha is not */
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for (chan = 0; chan < 3; chan++) {
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unsigned chan_bits = dst_fmt->channel[dst_fmt->swizzle[chan]].size;
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tmpsrgb[chan] = lp_build_linear_to_srgb(gallivm, src_type, chan_bits, src[chan]);
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}
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/*
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* can't use lp_build_conv since we want to keep values as 32bit
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* here so we can interleave with rgb to go from SoA->AoS.
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*/
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alpha = lp_build_clamp_zero_one_nanzero(&f32_bld, src[3]);
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alpha = lp_build_mul(&f32_bld, alpha,
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lp_build_const_vec(gallivm, src_type, 255.0f));
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tmpsrgb[3] = lp_build_iround(&f32_bld, alpha);
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dst = lp_build_zero(gallivm, int32_type);
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for (chan = 0; chan < dst_fmt->nr_channels; chan++) {
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if (dst_fmt->swizzle[chan] <= PIPE_SWIZZLE_W) {
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unsigned ls;
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LLVMValueRef shifted, shift_val;
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ls = dst_fmt->channel[dst_fmt->swizzle[chan]].shift;
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shift_val = lp_build_const_int_vec(gallivm, int32_type, ls);
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shifted = LLVMBuildShl(builder, tmpsrgb[chan], shift_val, "");
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dst = LLVMBuildOr(builder, dst, shifted, "");
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}
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}
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return dst;
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}
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