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/**************************************************************************

 *

 * Copyright 2013 VMware, Inc.

 * All Rights Reserved.

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 * The above copyright notice and this permission notice (including the

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/**

 * @file

 * Format conversion code for srgb formats.

 *

 * Functions for converting from srgb to linear and vice versa.

 * From http://www.opengl.org/registry/specs/EXT/texture_sRGB.txt:

 *

 * srgb->linear:

 * cl = cs / 12.92,                 cs <= 0.04045

 * cl = ((cs + 0.055)/1.055)^2.4,   cs >  0.04045

 *

 * linear->srgb:

 * if (isnan(cl)) {

 *    Map IEEE-754 Not-a-number to zero.

 *    cs = 0.0;

 * } else if (cl > 1.0) {

 *    cs = 1.0;

 * } else if (cl < 0.0) {

 *    cs = 0.0;

 * } else if (cl < 0.0031308) {

 *    cs = 12.92 * cl;

 * } else {

 *    cs = 1.055 * pow(cl, 0.41666) - 0.055;

 * }

 *

 * This does not need to be accurate, however at least for d3d10

 * (http://msdn.microsoft.com/en-us/library/windows/desktop/dd607323%28v=vs.85%29.aspx):

 * 1) For srgb->linear, it is required that the error on the srgb side is

 *    not larger than 0.5f, which I interpret that if you map the value back

 *    to srgb from linear using the ideal conversion, it would not be off by

 *    more than 0.5f (that is, it would map to the same 8-bit integer value

 *    as it was before conversion to linear).

 * 2) linear->srgb is permitted 0.6f which luckily looks like quite a large

 *    error is allowed.

 * 3) Additionally, all srgb values converted to linear and back must result

 *    in the same value as they were originally.

 *

 * @author Roland Scheidegger 

 */

#include "util/u_debug.h"

#include "lp_bld_type.h"

#include "lp_bld_const.h"

#include "lp_bld_arit.h"

#include "lp_bld_bitarit.h"

#include "lp_bld_logic.h"

#include "lp_bld_format.h"

/**

 * Convert srgb int values to linear float values.

 * Several possibilities how to do this, e.g.

 * - table

 * - doing the pow() with int-to-float and float-to-int tricks

 *   (http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent)

 * - just using standard polynomial approximation

 *   (3rd order polynomial is required for crappy but just sufficient accuracy)

 *

 * @param src   integer (vector) value(s) to convert

 *              (8 bit values unpacked to 32 bit already).

 */

LLVMValueRef

lp_build_srgb_to_linear(struct gallivm_state *gallivm,

                        struct lp_type src_type,

                        LLVMValueRef src)

{

   struct lp_type f32_type = lp_type_float_vec(32, src_type.length * 32);

   struct lp_build_context f32_bld;

   LLVMValueRef srcf, part_lin, part_pow, is_linear, lin_const, lin_thresh;

   double coeffs[4] = {0.0023f,

                       0.0030f / 255.0f,

                       0.6935f / (255.0f * 255.0f),

                       0.3012f / (255.0f * 255.0f * 255.0f)

   };

   assert(src_type.width == 32);

   lp_build_context_init(&f32_bld, gallivm, f32_type);

   /*

    * using polynomial: (src * (src * (src * 0.3012 + 0.6935) + 0.0030) + 0.0023)

    * ( poly =  0.3012*x^3 + 0.6935*x^2 + 0.0030*x + 0.0023)

    * (found with octave polyfit and some magic as I couldn't get the error

    * function right). Using the above mentioned error function, the values stay

    * within +-0.35, except for the lowest values - hence tweaking linear segment

    * to cover the first 16 instead of the first 11 values (the error stays

    * just about acceptable there too).

    * Hence: lin = src > 15 ? poly : src / 12.6

    * This function really only makes sense for vectors, should use LUT otherwise.

    * All in all (including float conversion) 11 instructions (with sse4.1),

    * 6 constants (polynomial could be done with 1 instruction less at the cost

    * of slightly worse dependency chain, fma should also help).

    */

   /* doing the 1/255 mul as part of the approximation */

   srcf = lp_build_int_to_float(&f32_bld, src);

   lin_const = lp_build_const_vec(gallivm, f32_type, 1.0f / (12.6f * 255.0f));

   part_lin = lp_build_mul(&f32_bld, srcf, lin_const);

   part_pow = lp_build_polynomial(&f32_bld, srcf, coeffs, 4);

   lin_thresh = lp_build_const_vec(gallivm, f32_type, 15.0f);

   is_linear = lp_build_compare(gallivm, f32_type, PIPE_FUNC_LEQUAL, srcf, lin_thresh);

   return lp_build_select(&f32_bld, is_linear, part_lin, part_pow);

}

/**

 * Convert linear float values to srgb int values.

 * Several possibilities how to do this, e.g.

 * - use table (based on exponent/highest order mantissa bits) and do

 *   linear interpolation (https://gist.github.com/rygorous/2203834)

 * - Chebyshev polynomial

 * - Approximation using reciprocals

 * - using int-to-float and float-to-int tricks for pow()

 *   (http://stackoverflow.com/questions/6475373/optimizations-for-pow-with-const-non-integer-exponent)

 *

 * @param src   float (vector) value(s) to convert.

 */

static LLVMValueRef

lp_build_linear_to_srgb(struct gallivm_state *gallivm,

                        struct lp_type src_type,

                        LLVMValueRef src)

{

   LLVMBuilderRef builder = gallivm->builder;

   struct lp_build_context f32_bld;

   LLVMValueRef lin_thresh, lin, lin_const, is_linear, tmp, pow_final;

   lp_build_context_init(&f32_bld, gallivm, src_type);

   src = lp_build_clamp(&f32_bld, src, f32_bld.zero, f32_bld.one);

   if (0) {

      /*

       * using int-to-float and float-to-int trick for pow().

       * This is much more accurate than necessary thanks to the correction,

       * but it most certainly makes no sense without rsqrt available.

       * Bonus points if you understand how this works...

       * All in all (including min/max clamp, conversion) 19 instructions.

       */

      float exp_f = 2.0f / 3.0f;

      /* some compilers can't do exp2f, so this is exp2f(127.0f/exp_f - 127.0f) */

      float exp2f_c = 1.30438178253e+19f;

      float coeff_f = 0.62996f;

      LLVMValueRef pow_approx, coeff, x2, exponent, pow_1, pow_2;

      struct lp_type int_type = lp_int_type(src_type);

      /*

       * First calculate approx x^8/12

       */

      exponent = lp_build_const_vec(gallivm, src_type, exp_f);

      coeff = lp_build_const_vec(gallivm, src_type,

                                 exp2f_c * powf(coeff_f, 1.0f / exp_f));

      /* premultiply src */

      tmp = lp_build_mul(&f32_bld, coeff, src);

      /* "log2" */

      tmp = LLVMBuildBitCast(builder, tmp, lp_build_vec_type(gallivm, int_type), "");

      tmp = lp_build_int_to_float(&f32_bld, tmp);

      /* multiply for pow */

      tmp = lp_build_mul(&f32_bld, tmp, exponent);

      /* "exp2" */

      pow_approx = lp_build_itrunc(&f32_bld, tmp);

      pow_approx = LLVMBuildBitCast(builder, pow_approx,

                                    lp_build_vec_type(gallivm, src_type), "");

      /*

       * Since that pow was inaccurate (like 3 bits, though each sqrt step would

       * give another bit), compensate the error (which is why we chose another

       * exponent in the first place).

       */

      /* x * x^(8/12) = x^(20/12) */

      pow_1 = lp_build_mul(&f32_bld, pow_approx, src);

      /* x * x * x^(-4/12) = x^(20/12) */

      /* Should avoid using rsqrt if it's not available, but

       * using x * x^(4/12) * x^(4/12) instead will change error weight */

      tmp = lp_build_fast_rsqrt(&f32_bld, pow_approx);

      x2 = lp_build_mul(&f32_bld, src, src);

      pow_2 = lp_build_mul(&f32_bld, x2, tmp);

      /* average the values so the errors cancel out, compensate bias,

       * we also squeeze the 1.055 mul of the srgb conversion plus the 255.0 mul

       * for conversion to int in here */

      tmp = lp_build_add(&f32_bld, pow_1, pow_2);

      coeff = lp_build_const_vec(gallivm, src_type,

                                 1.0f / (3.0f * coeff_f) * 0.999852f *

                                 powf(1.055f * 255.0f, 4.0f));

      pow_final = lp_build_mul(&f32_bld, tmp, coeff);

      /* x^(5/12) = rsqrt(rsqrt(x^20/12)) */

      if (lp_build_fast_rsqrt_available(src_type)) {

         pow_final = lp_build_fast_rsqrt(&f32_bld,

                        lp_build_fast_rsqrt(&f32_bld, pow_final));

      }

      else {

         pow_final = lp_build_sqrt(&f32_bld, lp_build_sqrt(&f32_bld, pow_final));

      }

      pow_final = lp_build_add(&f32_bld, pow_final,

                               lp_build_const_vec(gallivm, src_type, -0.055f * 255.0f));

   }

   else {

      /*

       * using "rational polynomial" approximation here.

       * Essentially y = a*x^0.375 + b*x^0.5 + c, with also

       * factoring in the 255.0 mul and the scaling mul.

       * (a is closer to actual value so has higher weight than b.)

       * Note: the constants are magic values. They were found empirically,

       * possibly could be improved but good enough (be VERY careful with

       * error metric if you'd want to tweak them, they also MUST fit with

       * the crappy polynomial above for srgb->linear since it is required

       * that each srgb value maps back to the same value).

       * This function has an error of max +-0.17 (and we'd only require +-0.6),

       * for the approximated srgb->linear values the error is naturally larger

       * (+-0.42) but still accurate enough (required +-0.5 essentially).

       * All in all (including min/max clamp, conversion) 15 instructions.

       * FMA would help (minus 2 instructions).

       */

      LLVMValueRef x05, x0375, a_const, b_const, c_const, tmp2;

      if (lp_build_fast_rsqrt_available(src_type)) {

         tmp = lp_build_fast_rsqrt(&f32_bld, src);

         x05 = lp_build_mul(&f32_bld, src, tmp);

      }

      else {

         /*

          * I don't really expect this to be practical without rsqrt

          * but there's no reason for triple punishment so at least

          * save the otherwise resulting division and unnecessary mul...

          */

         x05 = lp_build_sqrt(&f32_bld, src);

      }

      tmp = lp_build_mul(&f32_bld, x05, src);

      if (lp_build_fast_rsqrt_available(src_type)) {

         x0375 = lp_build_fast_rsqrt(&f32_bld, lp_build_fast_rsqrt(&f32_bld, tmp));

      }

      else {

         x0375 = lp_build_sqrt(&f32_bld, lp_build_sqrt(&f32_bld, tmp));

      }

      a_const = lp_build_const_vec(gallivm, src_type, 0.675f * 1.0622 * 255.0f);

      b_const = lp_build_const_vec(gallivm, src_type, 0.325f * 1.0622 * 255.0f);

      c_const = lp_build_const_vec(gallivm, src_type, -0.0620f * 255.0f);

      tmp = lp_build_mul(&f32_bld, a_const, x0375);

      tmp2 = lp_build_mul(&f32_bld, b_const, x05);

      tmp2 = lp_build_add(&f32_bld, tmp2, c_const);

      pow_final = lp_build_add(&f32_bld, tmp, tmp2);

   }

   /* linear part is easy */

   lin_const = lp_build_const_vec(gallivm, src_type, 12.92f * 255.0f);

   lin = lp_build_mul(&f32_bld, src, lin_const);

   lin_thresh = lp_build_const_vec(gallivm, src_type, 0.0031308f);

   is_linear = lp_build_compare(gallivm, src_type, PIPE_FUNC_LEQUAL, src, lin_thresh);

   tmp = lp_build_select(&f32_bld, is_linear, lin, pow_final);

   f32_bld.type.sign = 0;

   return lp_build_iround(&f32_bld, tmp);

}

/**

 * Convert linear float soa values to packed srgb AoS values.

 * This only handles packed formats which are 4x8bit in size

 * (rgba and rgbx plus swizzles).

 *

 * @param src   float SoA (vector) values to convert.

 */

LLVMValueRef

lp_build_float_to_srgb_packed(struct gallivm_state *gallivm,

                              const struct util_format_description *dst_fmt,

                              struct lp_type src_type,

                              LLVMValueRef *src)

{

   LLVMBuilderRef builder = gallivm->builder;

   unsigned chan;

   struct lp_build_context f32_bld;

   struct lp_type int32_type = lp_int_type(src_type);

   LLVMValueRef tmpsrgb[4], alpha, dst;

   lp_build_context_init(&f32_bld, gallivm, src_type);

   /* rgb is subject to linear->srgb conversion, alpha is not */

   for (chan = 0; chan < 3; chan++) {

      tmpsrgb[chan] = lp_build_linear_to_srgb(gallivm, src_type, src[chan]);

   }

   /*

    * can't use lp_build_conv since we want to keep values as 32bit

    * here so we can interleave with rgb to go from SoA->AoS.

    */

   alpha = lp_build_clamp(&f32_bld, src[3], f32_bld.zero, f32_bld.one);

   alpha = lp_build_mul(&f32_bld, alpha,

                        lp_build_const_vec(gallivm, src_type, 255.0f));

   tmpsrgb[3] = lp_build_iround(&f32_bld, alpha);

   dst = lp_build_zero(gallivm, int32_type);

   for (chan = 0; chan < dst_fmt->nr_channels; chan++) {

      if (dst_fmt->swizzle[chan] <= UTIL_FORMAT_SWIZZLE_W) {

         unsigned ls;

         LLVMValueRef shifted, shift_val;

         ls = dst_fmt->channel[dst_fmt->swizzle[chan]].shift;

         shift_val = lp_build_const_int_vec(gallivm, int32_type, ls);

         shifted = LLVMBuildShl(builder, tmpsrgb[chan], shift_val, "");

         dst = LLVMBuildOr(builder, dst, shifted, "");

      }

   }

   return dst;

}