DataFormats/Math/src/libminifloat.cc - master - githubmirror/cmssw

DataFormats/Math/src/libminifloat.cc
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11 июн 2019, 11:29
11 июн 2019, 11:29146bc98
#include "DataFormats/Math/interface/libminifloat.h"

namespace {
  MiniFloatConverter dummy;  // so the constructor is called
}
uint32_t MiniFloatConverter::mantissatable[2048];
uint32_t MiniFloatConverter::exponenttable[64];
uint16_t MiniFloatConverter::offsettable[64];
uint16_t MiniFloatConverter::basetable[512];
uint8_t MiniFloatConverter::shifttable[512];

MiniFloatConverter::MiniFloatConverter() {
  static bool once = false;
  if (!once) {
    filltables();
    once = true;
  }
}

void MiniFloatConverter::filltables() {
  // ==== mantissatable ===
  // -- zero --
  mantissatable[0] = 0;
  // -- denorm --
  for (unsigned int i = 1; i <= 1023; ++i) {
    unsigned int m = (i << 13), e = 0;
    while (!(m & 0x00800000)) {  // While not normalized
      e -= 0x00800000;           // Decrement exponent (1<<23)
      m <<= 1;                   // Shift mantissa
    }
    m &= ~0x00800000;  // Clear leading 1 bit
    e += 0x38800000;   // Adjust bias ((127-14)<<23)
    mantissatable[i] = m | e;
  }
  // -- norm --
  for (unsigned int i = 1024; i <= 2047; ++i) {
    mantissatable[i] = 0x38000000 + ((i - 1024) << 13);
  }
  // ==== exponenttable ===
  exponenttable[0] = 0;
  for (unsigned int i = 1; i <= 30; ++i)
    exponenttable[i] = i << 23;
  exponenttable[31] = 0x47800000;
  exponenttable[32] = 0x80000000u;
  for (unsigned int i = 33; i <= 62; ++i)
    exponenttable[i] = 0x80000000u | ((i - 32) << 23);
  exponenttable[63] = 0xC7800000;

  // ==== offsettable ====
  for (unsigned int i = 0; i <= 63; ++i)
    offsettable[i] = ((i == 0 || i == 32) ? 0 : 1024);

  // ==== basetable, shifttable ===
  for (unsigned i = 0; i < 256; ++i) {
    int e = int(i) - 127;
    if (e < -24) {  // Very small numbers map to zero
      basetable[i | 0x000] = 0x0000;
      basetable[i | 0x100] = 0x8000;
      shifttable[i | 0x000] = 24;
      shifttable[i | 0x100] = 24;
    } else if (e < -14) {  // Small numbers map to denorms
      basetable[i | 0x000] = (0x0400 >> (-e - 14));
      basetable[i | 0x100] = (0x0400 >> (-e - 14)) | 0x8000;
      shifttable[i | 0x000] = -e - 1;
      shifttable[i | 0x100] = -e - 1;
    } else if (e <= 15) {  // Normal numbers just lose precision
      basetable[i | 0x000] = ((e + 15) << 10);
      basetable[i | 0x100] = ((e + 15) << 10) | 0x8000;
      shifttable[i | 0x000] = 13;
      shifttable[i | 0x100] = 13;
    } else if (e < 128) {  // Large numbers map to Infinity
      basetable[i | 0x000] = 0x7C00;
      basetable[i | 0x100] = 0xFC00;
      shifttable[i | 0x000] = 24;
      shifttable[i | 0x100] = 24;
    } else {  // Infinity and NaN's stay Infinity and NaN's
      basetable[i | 0x000] = 0x7C00;
      basetable[i | 0x100] = 0xFC00;
      shifttable[i | 0x000] = 13;
      shifttable[i | 0x100] = 13;
    }
  }
}