lp_bld_format_float.c

/**************************************************************************
 *
 * 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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 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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/**
 * @file
 * Format conversion code for "special" float formats.
 *
 * @author Roland Scheidegger <[email protected]>
 */


#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 float32 to a float-like value with less exponent and mantissa
 * bits. The mantissa is still biased, and the mantissa still has an implied 1,
 * and there may be a sign bit.
 *
 * @param src             (vector) float value to convert
 * @param mantissa_bits   the number of mantissa bits
 * @param exponent_bits   the number of exponent bits
 * @param mantissa_start  the start position of the small float in result value
 * @param has_sign        if the small float has a sign bit
 *
 * This implements round-towards-zero (trunc) hence too large numbers get
 * converted to largest representable number, not infinity.
 * Small numbers may get converted to denorms, depending on normal
 * float denorm handling of the cpu.
 * Note that compared to the references, below, we skip any rounding bias
 * since we do rounding towards zero - OpenGL allows rounding towards zero
 * (though not preferred) and DX10 even seems to require it.
 * Note that this will pack mantissa, exponent and sign bit (if any) together,
 * and shift the result to mantissa_start.
 *
 * ref http://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
 * ref https://gist.github.com/rygorous/2156668
 */
LLVMValueRef
lp_build_float_to_smallfloat(struct gallivm_state *gallivm,
                             struct lp_type i32_type,
                             LLVMValueRef src,
                             unsigned mantissa_bits,
                             unsigned exponent_bits,
                             unsigned mantissa_start,
                             boolean has_sign)
{
   LLVMBuilderRef builder = gallivm->builder;
   LLVMValueRef i32_floatexpmask, i32_smallexpmask, magic, normal;
   LLVMValueRef rescale_src, i32_roundmask, small_max;
   LLVMValueRef i32_qnanbit, shift, res;
   LLVMValueRef is_nan_or_inf, nan_or_inf, mask, i32_src;
   struct lp_type f32_type = lp_type_float_vec(32, 32 * i32_type.length);
   struct lp_build_context f32_bld, i32_bld;
   LLVMValueRef zero = lp_build_const_vec(gallivm, f32_type, 0.0f);
   unsigned exponent_start = mantissa_start + mantissa_bits;
   boolean always_preserve_nans = true;
   boolean maybe_correct_denorm_rounding = true;

   lp_build_context_init(&f32_bld, gallivm, f32_type);
   lp_build_context_init(&i32_bld, gallivm, i32_type);

   i32_smallexpmask = lp_build_const_int_vec(gallivm, i32_type,
                                             ((1 << exponent_bits) - 1) << 23);
   i32_floatexpmask = lp_build_const_int_vec(gallivm, i32_type, 0xff << 23);

   i32_src = LLVMBuildBitCast(builder, src, i32_bld.vec_type, "");

   if (has_sign) {
      rescale_src = src;
   }
   else {
      /* clamp to pos range (can still have sign bit if NaN or negative zero) */
      rescale_src = lp_build_max(&f32_bld, zero, src);
   }
   rescale_src = LLVMBuildBitCast(builder, rescale_src, i32_bld.vec_type, "");

   /* "ordinary" number */
   /*
    * get rid of excess mantissa bits and sign bit
    * This is only really needed for correct rounding of denorms I think
    * but only if we use the preserve NaN path does using
    * src_abs instead save us any instruction.
    */
   if (maybe_correct_denorm_rounding || !always_preserve_nans) {
      i32_roundmask = lp_build_const_int_vec(gallivm, i32_type,
                                             ~((1 << (23 - mantissa_bits)) - 1) &
                                             0x7fffffff);
      rescale_src = LLVMBuildBitCast(builder, rescale_src, i32_bld.vec_type, "");
      rescale_src = lp_build_and(&i32_bld, rescale_src, i32_roundmask);
      rescale_src = LLVMBuildBitCast(builder, rescale_src, f32_bld.vec_type, "");
   }
   else {
      rescale_src = lp_build_abs(&f32_bld, src);
   }

   /* bias exponent (and denormalize if necessary) */
   magic = lp_build_const_int_vec(gallivm, i32_type,
                                  ((1 << (exponent_bits - 1)) - 1) << 23);
   magic = LLVMBuildBitCast(builder, magic, f32_bld.vec_type, "");
   normal = lp_build_mul(&f32_bld, rescale_src, magic);

   /* clamp to max value - largest non-infinity number */
   small_max = lp_build_const_int_vec(gallivm, i32_type,
                                      (((1 << exponent_bits) - 2) << 23) |
                                      (((1 << mantissa_bits) - 1) << (23 - mantissa_bits)));
   small_max = LLVMBuildBitCast(builder, small_max, f32_bld.vec_type, "");
   normal = lp_build_min(&f32_bld, normal, small_max);
   normal = LLVMBuildBitCast(builder, normal, i32_bld.vec_type, "");

   /*
    * handle nan/inf cases
    * a little bit tricky since -Inf -> 0, +Inf -> +Inf, +-Nan -> +Nan
    * (for no sign) else ->Inf -> ->Inf too.
    * could use explicit "unordered" comparison checking for NaNs
    * which might save us from calculating src_abs too.
    * (Cannot actually save the comparison since we need to distinguish
    * Inf and NaN cases anyway, but it would be better for AVX.)
    */
   if (always_preserve_nans) {
      LLVMValueRef infcheck_src, is_inf, is_nan;
      LLVMValueRef src_abs = lp_build_abs(&f32_bld, src);
      src_abs = LLVMBuildBitCast(builder, src_abs, i32_bld.vec_type, "");

      if (has_sign) {
         infcheck_src = src_abs;
      }
      else {
         infcheck_src = i32_src;
      }
      is_nan = lp_build_compare(gallivm, i32_type, PIPE_FUNC_GREATER,
                                src_abs, i32_floatexpmask);
      is_inf = lp_build_compare(gallivm, i32_type, PIPE_FUNC_EQUAL,
                                infcheck_src, i32_floatexpmask);
      is_nan_or_inf = lp_build_or(&i32_bld, is_nan, is_inf);
      /* could also set more mantissa bits but need at least the highest mantissa bit */
      i32_qnanbit = lp_build_const_vec(gallivm, i32_type, 1 << 22);
      /* combine maxexp with qnanbit */
      nan_or_inf = lp_build_or(&i32_bld, i32_smallexpmask,
                               lp_build_and(&i32_bld, is_nan, i32_qnanbit));
   }
   else {
      /*
       * A couple simplifications, with mostly 2 drawbacks (so disabled):
       * - it will promote some SNaNs (those which only had bits set
       * in the mantissa part which got chopped off) to +-Infinity.
       * (Those bits get chopped off anyway later so can as well use
       * rescale_src instead of src_abs here saving the calculation of that.)
       * - for no sign case, it relies on the max() being used for rescale_src
       * to give back the NaN (which is NOT ieee754r behavior, but should work
       * with sse2 on a full moon (rather if I got the operand order right) -
       * we _don't_ have well-defined behavior specified with min/max wrt NaNs,
       * however, and if it gets converted to cmp/select it may not work (we
       * don't really have specified behavior for cmp wrt NaNs neither).
       */
      rescale_src = LLVMBuildBitCast(builder, rescale_src, i32_bld.vec_type, "");
      is_nan_or_inf = lp_build_compare(gallivm, i32_type, PIPE_FUNC_GEQUAL,
                                       rescale_src, i32_floatexpmask);
      /* note this will introduce excess exponent bits */
      nan_or_inf = rescale_src;
   }
   res = lp_build_select(&i32_bld, is_nan_or_inf, nan_or_inf, normal);

   if (mantissa_start > 0 || !always_preserve_nans) {
      /* mask off excess bits */
      unsigned maskbits = (1 << (mantissa_bits + exponent_bits)) - 1;
      mask = lp_build_const_int_vec(gallivm, i32_type,
                                    maskbits << (23 - mantissa_bits));
      res = lp_build_and(&i32_bld, res, mask);
   }

   /* add back sign bit at right position */
   if (has_sign) {
      LLVMValueRef sign;
      struct lp_type u32_type = lp_type_uint_vec(32, 32 * i32_type.length);
      struct lp_build_context u32_bld;
      lp_build_context_init(&u32_bld, gallivm, u32_type);

      mask = lp_build_const_int_vec(gallivm, i32_type, 0x80000000);
      shift = lp_build_const_int_vec(gallivm, i32_type, 8 - exponent_bits);
      sign = lp_build_and(&i32_bld, mask, i32_src);
      sign = lp_build_shr(&u32_bld, sign, shift);
      res = lp_build_or(&i32_bld, sign, res);
   }

   /* shift to final position */
   if (exponent_start < 23) {
      shift = lp_build_const_int_vec(gallivm, i32_type, 23 - exponent_start);
      res = lp_build_shr(&i32_bld, res, shift);
   }
   else {
      shift = lp_build_const_int_vec(gallivm, i32_type, exponent_start - 23);
      res = lp_build_shl(&i32_bld, res, shift);
   }
   return res;
}


/**
 * Convert rgba float SoA values to packed r11g11b10 values.
 *
 * @param src   SoA float (vector) values to convert.
 */
LLVMValueRef
lp_build_float_to_r11g11b10(struct gallivm_state *gallivm,
                            const LLVMValueRef *src)
{
   LLVMValueRef dst, rcomp, bcomp, gcomp;
   struct lp_build_context i32_bld;
   LLVMTypeRef src_type = LLVMTypeOf(*src);
   unsigned src_length = LLVMGetTypeKind(src_type) == LLVMVectorTypeKind ?
                            LLVMGetVectorSize(src_type) : 1;
   struct lp_type i32_type = lp_type_int_vec(32, 32 * src_length);

   lp_build_context_init(&i32_bld, gallivm, i32_type);

   /* "rescale" and put in right position */
   rcomp = lp_build_float_to_smallfloat(gallivm, i32_type, src[0], 6, 5, 0, false);
   gcomp = lp_build_float_to_smallfloat(gallivm, i32_type, src[1], 6, 5, 11, false);
   bcomp = lp_build_float_to_smallfloat(gallivm, i32_type, src[2], 5, 5, 22, false);

   /* combine the values */
   dst = lp_build_or(&i32_bld, rcomp, gcomp);
   return lp_build_or(&i32_bld, dst, bcomp);
}


/**
 * Convert a float-like value with less exponent and mantissa
 * bits than a normal float32 to a float32. The mantissa of
 * the source value is assumed to have an implied 1, and the exponent
 * is biased. There may be a sign bit.
 * The source value to extract must be in a 32bit int (bits not part of
 * the value to convert will be masked off).
 * This works for things like 11-bit floats or half-floats,
 * mantissa, exponent (and sign if present) must be packed
 * the same as they are in a ordinary float.
 *
 * @param src             (vector) value to convert
 * @param mantissa_bits   the number of mantissa bits
 * @param exponent_bits   the number of exponent bits
 * @param mantissa_start  the bit start position of the packed component
 * @param has_sign        if the small float has a sign bit
 *
 * ref http://fgiesen.wordpress.com/2012/03/28/half-to-float-done-quic/
 * ref https://gist.github.com/rygorous/2156668
 */
LLVMValueRef
lp_build_smallfloat_to_float(struct gallivm_state *gallivm,
                             struct lp_type f32_type,
                             LLVMValueRef src,
                             unsigned mantissa_bits,
                             unsigned exponent_bits,
                             unsigned mantissa_start,
                             boolean has_sign)
{
   LLVMBuilderRef builder = gallivm->builder;
   LLVMValueRef smallexpmask, i32_floatexpmask, magic;
   LLVMValueRef wasinfnan, tmp, res, shift, maskabs, srcabs, sign;
   unsigned exponent_start = mantissa_start + mantissa_bits;
   struct lp_type i32_type = lp_type_int_vec(32, 32 * f32_type.length);
   struct lp_build_context f32_bld, i32_bld;

   lp_build_context_init(&f32_bld, gallivm, f32_type);
   lp_build_context_init(&i32_bld, gallivm, i32_type);

   /* extract the component to "float position" */
   if (exponent_start < 23) {
      shift = lp_build_const_int_vec(gallivm, i32_type, 23 - exponent_start);
      src = lp_build_shl(&i32_bld, src, shift);
   }
   else {
      shift = lp_build_const_int_vec(gallivm, i32_type, exponent_start - 23);
      src = lp_build_shr(&i32_bld, src, shift);
   }
   maskabs = lp_build_const_int_vec(gallivm, i32_type,
                                    ((1 << (mantissa_bits + exponent_bits)) - 1)
                                    << (23 - mantissa_bits));
   srcabs = lp_build_and(&i32_bld, src, maskabs);

   /* now do the actual scaling */
   smallexpmask = lp_build_const_int_vec(gallivm, i32_type,
                                         ((1 << exponent_bits) - 1) << 23);
   i32_floatexpmask = lp_build_const_int_vec(gallivm, i32_type, 0xff << 23);

   if (0) {
     /*
      * Note that this code path, while simpler, will convert small
      * float denorms to floats according to current cpu denorm mode, if
      * denorms are disabled it will flush them to zero!
      * If cpu denorms are enabled, it should be faster though as long as
      * there's no denorms in the inputs, but if there are actually denorms
      * it's likely to be an order of magnitude slower (on x86 cpus).
      */

      srcabs = LLVMBuildBitCast(builder, srcabs, f32_bld.vec_type, "");

      /*
       * magic number has exponent new exp bias + (new exp bias - old exp bias),
       * mantissa is 0.
       */
      magic = lp_build_const_int_vec(gallivm, i32_type,
                                     (255 - (1 << (exponent_bits - 1))) << 23);
      magic = LLVMBuildBitCast(builder, magic, f32_bld.vec_type, "");

      /* adjust exponent and fix denorms */
      res = lp_build_mul(&f32_bld, srcabs, magic);

      /*
       * if exp was max (== NaN or Inf) set new exp to max (keep mantissa),
       * so a simple "or" will do (because exp adjust will leave mantissa intact)
       */
      /* use float compare (better for AVX 8-wide / no AVX2 but else should use int) */
      smallexpmask = LLVMBuildBitCast(builder, smallexpmask, f32_bld.vec_type, "");
      wasinfnan = lp_build_compare(gallivm, f32_type, PIPE_FUNC_GEQUAL, srcabs, smallexpmask);
      res = LLVMBuildBitCast(builder, res, i32_bld.vec_type, "");
      tmp = lp_build_and(&i32_bld, i32_floatexpmask, wasinfnan);
      res = lp_build_or(&i32_bld, tmp, res);
   }

   else {
      LLVMValueRef exp_one, isdenorm, denorm, normal, exp_adj;

      /* denorm (or zero) if exponent is zero */
      exp_one = lp_build_const_int_vec(gallivm, i32_type, 1 << 23);
      isdenorm = lp_build_cmp(&i32_bld, PIPE_FUNC_LESS, srcabs, exp_one);

      /* inf or nan if exponent is max */
      wasinfnan = lp_build_cmp(&i32_bld, PIPE_FUNC_GEQUAL, srcabs, smallexpmask);

      /* for denormal (or zero), add (== or) magic exp to mantissa (== srcabs) (as int)
       * then subtract it (as float).
       * Another option would be to just do inttofp then do a rescale mul.
       */
      magic = lp_build_const_int_vec(gallivm, i32_type,
                                     (127 - ((1 << (exponent_bits - 1)) - 2)) << 23);
      denorm = lp_build_or(&i32_bld, srcabs, magic);
      denorm = LLVMBuildBitCast(builder, denorm, f32_bld.vec_type, "");
      denorm = lp_build_sub(&f32_bld, denorm,
                            LLVMBuildBitCast(builder, magic, f32_bld.vec_type, ""));
      denorm = LLVMBuildBitCast(builder, denorm, i32_bld.vec_type, "");

      /* for normals, Infs, Nans fix up exponent */
      exp_adj = lp_build_const_int_vec(gallivm, i32_type,
                                      (127 - ((1 << (exponent_bits - 1)) - 1)) << 23);
      normal = lp_build_add(&i32_bld, srcabs, exp_adj);
      tmp = lp_build_and(&i32_bld, wasinfnan, i32_floatexpmask);
      normal = lp_build_or(&i32_bld, tmp, normal);

      res = lp_build_select(&i32_bld, isdenorm, denorm, normal);
   }

   if (has_sign) {
      LLVMValueRef signmask = lp_build_const_int_vec(gallivm, i32_type, 0x80000000);
      shift = lp_build_const_int_vec(gallivm, i32_type, 8 - exponent_bits);
      sign = lp_build_shl(&i32_bld, src, shift);
      sign = lp_build_and(&i32_bld, signmask, sign);
      res = lp_build_or(&i32_bld, res, sign);
   }

   return LLVMBuildBitCast(builder, res, f32_bld.vec_type, "");
}


/**
 * Convert packed float format (r11g11b10) value(s) to rgba float SoA values.
 *
 * @param src   packed AoS r11g11b10 values (as (vector) int32)
 * @param dst   pointer to the SoA result values
 */
void
lp_build_r11g11b10_to_float(struct gallivm_state *gallivm,
                            LLVMValueRef src,
                            LLVMValueRef *dst)
{
   LLVMTypeRef src_type = LLVMTypeOf(src);
   unsigned src_length = LLVMGetTypeKind(src_type) == LLVMVectorTypeKind ?
                            LLVMGetVectorSize(src_type) : 1;
   struct lp_type f32_type = lp_type_float_vec(32, 32 * src_length);

   dst[0] = lp_build_smallfloat_to_float(gallivm, f32_type, src, 6, 5, 0, false);
   dst[1] = lp_build_smallfloat_to_float(gallivm, f32_type, src, 6, 5, 11, false);
   dst[2] = lp_build_smallfloat_to_float(gallivm, f32_type, src, 5, 5, 22, false);

   /* Just set alpha to one */
   dst[3] = lp_build_one(gallivm, f32_type);
}


static LLVMValueRef
lp_build_rgb9_to_float_helper(struct gallivm_state *gallivm,
                              struct lp_type f32_type,
                              LLVMValueRef src,
                              LLVMValueRef scale,
                              unsigned mantissa_start)
{
   LLVMValueRef shift, mask;

   struct lp_type i32_type = lp_type_int_vec(32, 32 * f32_type.length);
   struct lp_build_context i32_bld, f32_bld;

   lp_build_context_init(&i32_bld, gallivm, i32_type);
   lp_build_context_init(&f32_bld, gallivm, f32_type);

   /*
    * This is much easier as other weirdo float formats, since
    * there's no sign, no Inf/NaN, and there's nothing special
    * required for normals/denormals neither (as without the implied one
    * for the mantissa for other formats, everything looks like a denormal).
    * So just do (float)comp_bits * scale
    */
   shift = lp_build_const_int_vec(gallivm, i32_type, mantissa_start);
   mask = lp_build_const_int_vec(gallivm, i32_type, 0x1ff);
   src = lp_build_shr(&i32_bld, src, shift);
   src = lp_build_and(&i32_bld, src, mask);
   src = lp_build_int_to_float(&f32_bld, src);
   return lp_build_mul(&f32_bld, src, scale);
}


/**
 * Convert shared exponent format (rgb9e5) value(s) to rgba float SoA values.
 *
 * @param src   packed AoS rgb9e5 values (as (vector) int32)
 * @param dst   pointer to the SoA result values
 */
void
lp_build_rgb9e5_to_float(struct gallivm_state *gallivm,
                         LLVMValueRef src,
                         LLVMValueRef *dst)
{
   LLVMBuilderRef builder = gallivm->builder;
   LLVMTypeRef src_type = LLVMTypeOf(src);
   LLVMValueRef shift, scale, bias, exp;
   unsigned src_length = LLVMGetTypeKind(src_type) == LLVMVectorTypeKind ?
                            LLVMGetVectorSize(src_type) : 1;
   struct lp_type i32_type = lp_type_int_vec(32, 32 * src_length);
   struct lp_type u32_type = lp_type_uint_vec(32, 32 * src_length);
   struct lp_type f32_type = lp_type_float_vec(32, 32 * src_length);
   struct lp_build_context i32_bld, u32_bld, f32_bld;

   lp_build_context_init(&i32_bld, gallivm, i32_type);
   lp_build_context_init(&u32_bld, gallivm, u32_type);
   lp_build_context_init(&f32_bld, gallivm, f32_type);

   /* extract exponent */
   shift = lp_build_const_int_vec(gallivm, i32_type, 27);
   /* this shift needs to be unsigned otherwise need mask */
   exp = lp_build_shr(&u32_bld, src, shift);

   /*
    * scale factor is 2 ^ (exp - bias)
    * (and additionally corrected here for the mantissa bits)
    * not using shift because
    * a) don't have vector shift in a lot of cases
    * b) shift direction changes hence need 2 shifts + conditional
    *    (or rotate instruction which is even more rare (for instance XOP))
    * so use whacky float 2 ^ function instead manipulating exponent
    * (saves us the float conversion at the end too)
    */
   bias = lp_build_const_int_vec(gallivm, i32_type, 127 - (15 + 9));
   scale = lp_build_add(&i32_bld, exp, bias);
   shift = lp_build_const_int_vec(gallivm, i32_type, 23);
   scale = lp_build_shl(&i32_bld, scale, shift);
   scale = LLVMBuildBitCast(builder, scale, f32_bld.vec_type, "");

   dst[0] = lp_build_rgb9_to_float_helper(gallivm, f32_type, src, scale, 0);
   dst[1] = lp_build_rgb9_to_float_helper(gallivm, f32_type, src, scale, 9);
   dst[2] = lp_build_rgb9_to_float_helper(gallivm, f32_type, src, scale, 18);

   /* Just set alpha to one */
   dst[3] = f32_bld.one;
}