Manual float 16 add

adding float16 bytes.ts

const byteMask = 0xff_ff;

function AddFloat16(a: number, b: number): number {
  a = a & byteMask;
  b = b & byteMask;
  const signA = a >> 15;
  const signB = b >> 15;
  let expA = (a >> 10) & 0b11111;
  let expB = (b >> 10) & 0b11111;
  let mantA = a & 0b1111111111;
  let mantB = b & 0b1111111111;

  if (expA === 0x1f && mantA !== 0) return a;
  if (expB === 0x1f && mantB !== 0) return b;
  if (expA === 0x1f && expB === 0x1f) {
    if (signA !== signB) {
      return 0x7e00;
    }
    return a;
  }
  if (expA === 0x1f) return a;
  if (expB === 0x1f) return b;

  mantA = mantA | 0x400;
  if (expA !== 0) {
    expA -= 1;
  }

  mantB = mantB | 0x400;
  if (expB !== 0) {
    expB -= 1;
  }

  if (expA > expB) {
    mantB = mantB >> (expA - expB);
    expB = expA;
  } else if (expB > expA) {
    mantA = mantA >> (expB - expA);
    expA = expB;
  }

  let resultMant: number;
  if (signA === signB) {
    resultMant = mantA + mantB;
  } else {
    resultMant = mantA - mantB;
  }

  let resultSign = signA;
  if (resultMant < 0) {
    resultSign = 1;
    resultMant = -resultMant;
  }

  let resultExp = expA + 1;
  while (resultMant >= 0x800) {
    resultMant = resultMant >> 1;
    resultExp += 1;
  }

  while (resultMant < 0x400 && resultExp > 0) {
    resultMant = resultMant << 1;
    resultExp -= 1;
  }

  if (resultExp >= 0x1f) {
    return (resultSign << 15) | 0x7c00;
  }
  if (resultExp === 0) {
    return (resultSign << 15) | (resultMant & 0x3ff);
  }

  return (resultSign << 15) | (resultExp << 10) | (resultMant & 0x3ff);
}

example.ts

const f16Arr = new Float16Array(1);
const i16Arr = new Int16Array(f16Arr.buffer);

f16Arr[0] = 7;
const a = i16Arr[0];

f16Arr[0] = 3;
const b = i16Arr[0];

i16Arr[0] = AddFloat16(a, b);

console.log(f16Arr[0]);