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bytes-utils.js
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113 lines (101 loc) · 2.57 KB
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const assert = require('assert');
function signum(a, b) {
return a < b ? -1 : a === b ? 0 : 1;
}
const hexLookup = (function() {
const res = {};
const reverse = res.reverse = new Array(256);
for (let i = 0; i < 16; i++) {
const char = i.toString(16).toUpperCase();
res[char] = i;
for (let j = 0; j < 16; j++) {
const char2 = j.toString(16).toUpperCase();
const byte = (i << 4) + j;
const byteHex = char + char2;
res[byteHex] = byte;
reverse[byte] = byteHex;
}
}
return res;
}());
const reverseHexLookup = hexLookup.reverse;
function bytesToHex(sequence) {
const buf = Array(sequence.length);
for (let i = sequence.length - 1; i >= 0; i--) {
buf[i] = reverseHexLookup[sequence[i]];
}
return buf.join('');
}
function byteForHex(hex) {
const byte = hexLookup[hex];
if (byte === undefined) {
throw new Error(`\`${hex}\` is not a valid hex representation of a byte`);
}
return byte;
}
function parseBytes(val, Output = Array) {
if (!val || val.length === undefined) {
throw new Error(`${val} is not a sequence`);
}
if (typeof val === 'string') {
const start = val.length % 2;
const res = new Output((val.length + start) / 2);
for (let i = val.length, to = res.length - 1; to >= start; i -= 2, to--) {
res[to] = byteForHex(val.slice(i - 2, i));
}
if (start === 1) {
res[0] = byteForHex(val[0]);
}
return res;
} else if (val instanceof Output) {
return val;
} else if (Output === Uint8Array) {
return new Output(val);
}
const res = new Output(val.length);
for (let i = val.length - 1; i >= 0; i--) {
res[i] = val[i];
}
return res;
}
function serializeUIntN(val, width) {
const newBytes = new Uint8Array(width);
const lastIx = width - 1;
for (let i = 0; i < width; i++) {
newBytes[lastIx - i] = (val >>> (i * 8) & 0xff);
}
return newBytes;
}
function compareBytes(a, b) {
assert(a.length === b.length);
for (let i = 0; i < a.length; i++) {
const cmp = signum(a[i], b[i]);
if (cmp !== 0) {
return cmp;
}
}
return 0;
}
function slice(val, startIx = 0, endIx = val.length, Output = val.constructor) {
/* eslint-disable no-param-reassign*/
if (startIx < 0) {
startIx += val.length;
}
if (endIx < 0) {
endIx += val.length;
}
/* eslint-enable no-param-reassign*/
const len = endIx - startIx;
const res = new Output(len);
for (let i = endIx - 1; i >= startIx; i--) {
res[i - startIx] = val[i];
}
return res;
}
module.exports = {
parseBytes,
bytesToHex,
slice,
compareBytes,
serializeUIntN
};