refactor

src/_util/converter.mjs

@@ -14,6 +14,11 @@ import {
  ObjectIs,
 } from "./primordials.mjs";
 
+const mantissaBitLength = 10;
+const mantissaMask = 0x3ff;
+const exponentMax = 31;
+const exponentBias = 15;
+
 // base algorithm: https://github.com/feross/ieee754
 // BSD-3-Clause License. Feross Aboukhadijeh <https://feross.org/opensource>
 
@@ -25,19 +30,13 @@ import {
  */
 function roundTiesToEven(num) {
  const truncated = MathTrunc(num);
- const isOdd = truncated % 2 !== 0;
  const delta = MathAbs(num - truncated);
- if (delta > 0.5 || delta === 0.5 && isOdd) {
+ if (delta > 0.5 || delta === 0.5 && truncated % 2 !== 0) {
  return truncated + MathSign(num);
  }
  return truncated;
 }
 
-const f16EMax = 31;
-const f16EBias = 15;
-const f16MLen = 10;
-const f16MMask = 0x3ff;
-
 /**
  * round a number to a half float number bits
  * @param {unknown} num - double float
@@ -52,7 +51,7 @@ export function roundToFloat16Bits(num) {
  // NaN, Infinity, -Infinity
  if (!NumberIsFinite(absNum)) {
  m = NumberIsNaN(absNum) ? 0x200 : 0;
- e = f16EMax;
+ e = exponentMax;
 
  // finite
  } else {
@@ -67,19 +66,19 @@ export function roundToFloat16Bits(num) {
  c /= 2;
  }
 
- if (rawE + f16EBias >= f16EMax) {
+ if (rawE + exponentBias >= exponentMax) {
  m = 0;
- e = f16EMax;
- } else if (rawE + f16EBias >= 1) {
- m = roundTiesToEven(((absNum * c) - 1) * 0x400) & f16MMask;
- e = rawE + f16EBias;
+ e = exponentMax;
+ } else if (rawE + exponentBias >= 1) {
+ m = roundTiesToEven(((absNum * c) - 1) * 0x400) & mantissaMask;
+ e = rawE + exponentBias;
  } else {
- m = roundTiesToEven(absNum * 0x1000000) & f16MMask;
+ m = roundTiesToEven(absNum * 0x1000000) & mantissaMask;
  e = 0;
  }
  }
 
- return s << 15 | e << f16MLen | m;
+ return s << 15 | e << mantissaBitLength | m;
 }
 
 // base algorithm: http://fox-toolkit.org/ftp/fasthalffloatconversion.pdf
@@ -132,7 +131,7 @@ for (let i = 1; i < 64; ++i) {
  * @returns {number} double float
  */
 export function convertToNumber(float16bits) {
- const i = float16bits >> 10;
- uint32View[0] = mantissaTable[offsetTable[i] + (float16bits & 0x3ff)] + exponentTable[i];
+ const i = float16bits >> mantissaBitLength;
+ uint32View[0] = mantissaTable[offsetTable[i] + (float16bits & mantissaMask)] + exponentTable[i];
  return floatView[0];
 }