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Last active February 24, 2020 08:43
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nextafter implemented in vanilla js without dependancies
// nextafter implemented in vanilla js without dependancies
// No license, use as you wish.
function nextafter(from, to){
if(isNaN(from) || isNaN(to))
return NaN;
if(from === to)
return to;
if(from === 0)
return (to > 0) ? Number.MIN_VALUE : -Number.MIN_VALUE;
const needToIncrement = (to > from) === (from > 0);
return incrementOrDecrementFloat(from, needToIncrement);
function incrementOrDecrementFloat(float, increment){
const floatFormat = new Float64Array(1);
const uintFormat = new Uint32Array(floatFormat.buffer);
const maxUint32Value = 0xFFFFFFFF;
floatFormat[0] = 1.0;
const littleEndian = uintFormat[0] === 0x3FF00000;
const highPart = littleEndian ? 0 : 1;
const lowPart = littleEndian ? 1 : 0;
floatFormat[0] = float;
if(increment){
if(uintFormat[lowPart] === maxUint32Value){
uintFormat[highPart]++;
uintFormat[lowPart] = 0;
}
else{
uintFormat[lowPart]++;
}
}
else{
if(uintFormat[lowPart] === 0){
uintFormat[highPart]--;
uintFormat[lowPart] = maxUint32Value;
}
else{
uintFormat[lowPart]--;
}
}
return floatFormat[0];
}
}
function testNextAfter(){
console.assert(nextafter(Infinity,Infinity) === Infinity);
console.assert(nextafter(Infinity,-1) === Number.MAX_VALUE);
console.assert(nextafter(-Infinity,+1) === -Number.MAX_VALUE);
console.assert(nextafter(-Infinity,-Infinity) === -Infinity);
console.assert(isNaN(nextafter(NaN, 0)));
console.assert(isNaN(nextafter(NaN, NaN)));
console.assert(isNaN(nextafter(0, NaN)));
console.assert(nextafter(0,1.33) === Number.MIN_VALUE);
console.assert(nextafter(0,-989) === -Number.MIN_VALUE);
console.assert(nextafter(-0,0) === 0);
console.assert(nextafter(1923,1) === 1922.9999999999998);
console.assert(nextafter(1923,1) === 1922.9999999999998);
console.assert(nextafter(-1123123,11) === -1123122.9999999998);
console.assert(nextafter(999.1233333,11111) === 999.1233333000001);
console.assert(nextafter(-10, -99) === -10.000000000000002);
}
function printFloatHex(float){
const floatFormat = new Float64Array(1);
const uintFormat = new Uint32Array(floatFormat.buffer);
floatFormat[0] = float;
console.log(uintFormat[1].toString(16).padStart(8, '0'), uintFormat[0].toString(16).padStart(8, '0'))
}
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