kc3-lang/angle/include/CL/cl_half.h

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• Author : Jamie Madill
  Date : 2021-02-19 17:28:10
  Hash : 6623a70f
  Message : Stubs for OpenCL entry points. Bug: angleproject:5653 Change-Id: I7ec9692a47be2556fef5bdd7630b422cc2d369b9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2708343 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com>

• include/CL/cl_half.h

• /*******************************************************************************
   * Copyright (c) 2019-2020 The Khronos Group Inc.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   ******************************************************************************/
  
  /**
   * This is a header-only utility library that provides OpenCL host code with
   * routines for converting to/from cl_half values.
   *
   * Example usage:
   *
   *    #include <CL/cl_half.h>
   *    ...
   *    cl_half h = cl_half_from_float(0.5f, CL_HALF_RTE);
   *    cl_float f = cl_half_to_float(h);
   */
  
  #ifndef OPENCL_CL_HALF_H
  #define OPENCL_CL_HALF_H
  
  #include <CL/cl_platform.h>
  
  #include <stdint.h>
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  
  /**
   * Rounding mode used when converting to cl_half.
   */
  typedef enum
  {
    CL_HALF_RTE, // round to nearest even
    CL_HALF_RTZ, // round towards zero
    CL_HALF_RTP, // round towards positive infinity
    CL_HALF_RTN, // round towards negative infinity
  } cl_half_rounding_mode;
  
  
  /* Private utility macros. */
  #define CL_HALF_EXP_MASK 0x7C00
  #define CL_HALF_MAX_FINITE_MAG 0x7BFF
  
  
  /*
   * Utility to deal with values that overflow when converting to half precision.
   */
  static inline cl_half cl_half_handle_overflow(cl_half_rounding_mode rounding_mode,
                                                uint16_t sign)
  {
    if (rounding_mode == CL_HALF_RTZ)
    {
      // Round overflow towards zero -> largest finite number (preserving sign)
      return (sign << 15) | CL_HALF_MAX_FINITE_MAG;
    }
    else if (rounding_mode == CL_HALF_RTP && sign)
    {
      // Round negative overflow towards positive infinity -> most negative finite number
      return (1 << 15) | CL_HALF_MAX_FINITE_MAG;
    }
    else if (rounding_mode == CL_HALF_RTN && !sign)
    {
      // Round positive overflow towards negative infinity -> largest finite number
      return CL_HALF_MAX_FINITE_MAG;
    }
  
    // Overflow to infinity
    return (sign << 15) | CL_HALF_EXP_MASK;
  }
  
  /*
   * Utility to deal with values that underflow when converting to half precision.
   */
  static inline cl_half cl_half_handle_underflow(cl_half_rounding_mode rounding_mode,
                                                 uint16_t sign)
  {
    if (rounding_mode == CL_HALF_RTP && !sign)
    {
      // Round underflow towards positive infinity -> smallest positive value
      return (sign << 15) | 1;
    }
    else if (rounding_mode == CL_HALF_RTN && sign)
    {
      // Round underflow towards negative infinity -> largest negative value
      return (sign << 15) | 1;
    }
  
    // Flush to zero
    return (sign << 15);
  }
  
  
  /**
   * Convert a cl_float to a cl_half.
   */
  static inline cl_half cl_half_from_float(cl_float f, cl_half_rounding_mode rounding_mode)
  {
    // Type-punning to get direct access to underlying bits
    union
    {
      cl_float f;
      uint32_t i;
    } f32;
    f32.f = f;
  
    // Extract sign bit
    uint16_t sign = f32.i >> 31;
  
    // Extract FP32 exponent and mantissa
    uint32_t f_exp = (f32.i >> (CL_FLT_MANT_DIG - 1)) & 0xFF;
    uint32_t f_mant = f32.i & ((1 << (CL_FLT_MANT_DIG - 1)) - 1);
  
    // Remove FP32 exponent bias
    int32_t exp = f_exp - CL_FLT_MAX_EXP + 1;
  
    // Add FP16 exponent bias
    uint16_t h_exp = (uint16_t)(exp + CL_HALF_MAX_EXP - 1);
  
    // Position of the bit that will become the FP16 mantissa LSB
    uint32_t lsb_pos = CL_FLT_MANT_DIG - CL_HALF_MANT_DIG;
  
    // Check for NaN / infinity
    if (f_exp == 0xFF)
    {
      if (f_mant)
      {
        // NaN -> propagate mantissa and silence it
        uint16_t h_mant = (uint16_t)(f_mant >> lsb_pos);
        h_mant |= 0x200;
        return (sign << 15) | CL_HALF_EXP_MASK | h_mant;
      }
      else
      {
        // Infinity -> zero mantissa
        return (sign << 15) | CL_HALF_EXP_MASK;
      }
    }
  
    // Check for zero
    if (!f_exp && !f_mant)
    {
      return (sign << 15);
    }
  
    // Check for overflow
    if (exp >= CL_HALF_MAX_EXP)
    {
      return cl_half_handle_overflow(rounding_mode, sign);
    }
  
    // Check for underflow
    if (exp < (CL_HALF_MIN_EXP - CL_HALF_MANT_DIG - 1))
    {
      return cl_half_handle_underflow(rounding_mode, sign);
    }
  
    // Check for value that will become denormal
    if (exp < -14)
    {
      // Denormal -> include the implicit 1 from the FP32 mantissa
      h_exp = 0;
      f_mant |= 1 << (CL_FLT_MANT_DIG - 1);
  
      // Mantissa shift amount depends on exponent
      lsb_pos = -exp + (CL_FLT_MANT_DIG - 25);
    }
  
    // Generate FP16 mantissa by shifting FP32 mantissa
    uint16_t h_mant = (uint16_t)(f_mant >> lsb_pos);
  
    // Check whether we need to round
    uint32_t halfway = 1 << (lsb_pos - 1);
    uint32_t mask = (halfway << 1) - 1;
    switch (rounding_mode)
    {
      case CL_HALF_RTE:
        if ((f_mant & mask) > halfway)
        {
          // More than halfway -> round up
          h_mant += 1;
        }
        else if ((f_mant & mask) == halfway)
        {
          // Exactly halfway -> round to nearest even
          if (h_mant & 0x1)
            h_mant += 1;
        }
        break;
      case CL_HALF_RTZ:
        // Mantissa has already been truncated -> do nothing
        break;
      case CL_HALF_RTP:
        if ((f_mant & mask) && !sign)
        {
          // Round positive numbers up
          h_mant += 1;
        }
        break;
      case CL_HALF_RTN:
        if ((f_mant & mask) && sign)
        {
          // Round negative numbers down
          h_mant += 1;
        }
        break;
    }
  
    // Check for mantissa overflow
    if (h_mant & 0x400)
    {
      h_exp += 1;
      h_mant = 0;
    }
  
    return (sign << 15) | (h_exp << 10) | h_mant;
  }
  
  
  /**
   * Convert a cl_double to a cl_half.
   */
  static inline cl_half cl_half_from_double(cl_double d, cl_half_rounding_mode rounding_mode)
  {
    // Type-punning to get direct access to underlying bits
    union
    {
      cl_double d;
      uint64_t i;
    } f64;
    f64.d = d;
  
    // Extract sign bit
    uint16_t sign = f64.i >> 63;
  
    // Extract FP64 exponent and mantissa
    uint64_t d_exp = (f64.i >> (CL_DBL_MANT_DIG - 1)) & 0x7FF;
    uint64_t d_mant = f64.i & (((uint64_t)1 << (CL_DBL_MANT_DIG - 1)) - 1);
  
    // Remove FP64 exponent bias
    int64_t exp = d_exp - CL_DBL_MAX_EXP + 1;
  
    // Add FP16 exponent bias
    uint16_t h_exp = (uint16_t)(exp + CL_HALF_MAX_EXP - 1);
  
    // Position of the bit that will become the FP16 mantissa LSB
    uint32_t lsb_pos = CL_DBL_MANT_DIG - CL_HALF_MANT_DIG;
  
    // Check for NaN / infinity
    if (d_exp == 0x7FF)
    {
      if (d_mant)
      {
        // NaN -> propagate mantissa and silence it
        uint16_t h_mant = (uint16_t)(d_mant >> lsb_pos);
        h_mant |= 0x200;
        return (sign << 15) | CL_HALF_EXP_MASK | h_mant;
      }
      else
      {
        // Infinity -> zero mantissa
        return (sign << 15) | CL_HALF_EXP_MASK;
      }
    }
  
    // Check for zero
    if (!d_exp && !d_mant)
    {
      return (sign << 15);
    }
  
    // Check for overflow
    if (exp >= CL_HALF_MAX_EXP)
    {
      return cl_half_handle_overflow(rounding_mode, sign);
    }
  
    // Check for underflow
    if (exp < (CL_HALF_MIN_EXP - CL_HALF_MANT_DIG - 1))
    {
      return cl_half_handle_underflow(rounding_mode, sign);
    }
  
    // Check for value that will become denormal
    if (exp < -14)
    {
      // Include the implicit 1 from the FP64 mantissa
      h_exp = 0;
      d_mant |= (uint64_t)1 << (CL_DBL_MANT_DIG - 1);
  
      // Mantissa shift amount depends on exponent
      lsb_pos = (uint32_t)(-exp + (CL_DBL_MANT_DIG - 25));
    }
  
    // Generate FP16 mantissa by shifting FP64 mantissa
    uint16_t h_mant = (uint16_t)(d_mant >> lsb_pos);
  
    // Check whether we need to round
    uint64_t halfway = (uint64_t)1 << (lsb_pos - 1);
    uint64_t mask = (halfway << 1) - 1;
    switch (rounding_mode)
    {
      case CL_HALF_RTE:
        if ((d_mant & mask) > halfway)
        {
          // More than halfway -> round up
          h_mant += 1;
        }
        else if ((d_mant & mask) == halfway)
        {
          // Exactly halfway -> round to nearest even
          if (h_mant & 0x1)
            h_mant += 1;
        }
        break;
      case CL_HALF_RTZ:
        // Mantissa has already been truncated -> do nothing
        break;
      case CL_HALF_RTP:
        if ((d_mant & mask) && !sign)
        {
          // Round positive numbers up
          h_mant += 1;
        }
        break;
      case CL_HALF_RTN:
        if ((d_mant & mask) && sign)
        {
          // Round negative numbers down
          h_mant += 1;
        }
        break;
    }
  
    // Check for mantissa overflow
    if (h_mant & 0x400)
    {
      h_exp += 1;
      h_mant = 0;
    }
  
    return (sign << 15) | (h_exp << 10) | h_mant;
  }
  
  
  /**
   * Convert a cl_half to a cl_float.
   */
  static inline cl_float cl_half_to_float(cl_half h)
  {
    // Type-punning to get direct access to underlying bits
    union
    {
      cl_float f;
      uint32_t i;
    } f32;
  
    // Extract sign bit
    uint16_t sign = h >> 15;
  
    // Extract FP16 exponent and mantissa
    uint16_t h_exp = (h >> (CL_HALF_MANT_DIG - 1)) & 0x1F;
    uint16_t h_mant = h & 0x3FF;
  
    // Remove FP16 exponent bias
    int32_t exp = h_exp - CL_HALF_MAX_EXP + 1;
  
    // Add FP32 exponent bias
    uint32_t f_exp = exp + CL_FLT_MAX_EXP - 1;
  
    // Check for NaN / infinity
    if (h_exp == 0x1F)
    {
      if (h_mant)
      {
        // NaN -> propagate mantissa and silence it
        uint32_t f_mant = h_mant << (CL_FLT_MANT_DIG - CL_HALF_MANT_DIG);
        f_mant |= 0x400000;
        f32.i = (sign << 31) | 0x7F800000 | f_mant;
        return f32.f;
      }
      else
      {
        // Infinity -> zero mantissa
        f32.i = (sign << 31) | 0x7F800000;
        return f32.f;
      }
    }
  
    // Check for zero / denormal
    if (h_exp == 0)
    {
      if (h_mant == 0)
      {
        // Zero -> zero exponent
        f_exp = 0;
      }
      else
      {
        // Denormal -> normalize it
        // - Shift mantissa to make most-significant 1 implicit
        // - Adjust exponent accordingly
        uint32_t shift = 0;
        while ((h_mant & 0x400) == 0)
        {
          h_mant <<= 1;
          shift++;
        }
        h_mant &= 0x3FF;
        f_exp -= shift - 1;
      }
    }
  
    f32.i = (sign << 31) | (f_exp << 23) | (h_mant << 13);
    return f32.f;
  }
  
  
  #undef CL_HALF_EXP_MASK
  #undef CL_HALF_MAX_FINITE_MAG
  
  
  #ifdef __cplusplus
  }
  #endif
  
  
  #endif  /* OPENCL_CL_HALF_H */