asn1-ts
Version:
ASN.1 encoding and decoding, including BER, CER, and DER.
109 lines (108 loc) • 5.45 kB
JavaScript
import * as errors from "../../../errors.mjs";
import { ASN1SpecialRealValue, ASN1RealEncodingBase, ASN1RealEncodingScale, nr1Regex, nr2Regex, nr3Regex, } from "../../../values.mjs";
import convertBytesToText from "../../../utils/convertBytesToText.mjs";
import decodeUnsignedBigEndianInteger from "../../../utils/decodeUnsignedBigEndianInteger.mjs";
import decodeSignedBigEndianInteger from "../../../utils/decodeSignedBigEndianInteger.mjs";
export default function decodeReal(value) {
if (value.length === 0)
return 0.0;
switch (value[0] & 0b11000000) {
case (0b01000000): {
if (value[0] === ASN1SpecialRealValue.notANumber)
return NaN;
if (value[0] === ASN1SpecialRealValue.minusZero)
return -0.0;
if (value[0] === ASN1SpecialRealValue.plusInfinity)
return Infinity;
if (value[0] === ASN1SpecialRealValue.minusInfinity)
return -Infinity;
throw new errors.ASN1UndefinedError("Unrecognized special REAL value!");
}
case (0b00000000): {
const realString = convertBytesToText(value.subarray(1));
switch (value[0] & 0b00111111) {
case 1: {
if (!nr1Regex.test(realString))
throw new errors.ASN1Error("Malformed NR1 Base-10 REAL");
return Number.parseFloat(realString);
}
case 2: {
if (!nr2Regex.test(realString))
throw new errors.ASN1Error("Malformed NR2 Base-10 REAL");
return Number.parseFloat(realString.replace(",", "."));
}
case 3: {
if (!nr3Regex.test(realString))
throw new errors.ASN1Error("Malformed NR3 Base-10 REAL");
return Number.parseFloat(realString.replace(",", "."));
}
default:
throw new errors.ASN1UndefinedError("Undefined Base-10 REAL encoding.");
}
}
case (0b10000000):
case (0b11000000): {
const sign = ((value[0] & 0b01000000) ? -1 : 1);
const base = ((flag) => {
switch (flag) {
case (ASN1RealEncodingBase.base2): return 2;
case (ASN1RealEncodingBase.base8): return 8;
case (ASN1RealEncodingBase.base16): return 16;
default:
throw new errors.ASN1Error("Impossible REAL encoding base encountered.");
}
})(value[0] & 0b00110000);
const scale = ((flag) => {
switch (flag) {
case (ASN1RealEncodingScale.scale0): return 0;
case (ASN1RealEncodingScale.scale1): return 1;
case (ASN1RealEncodingScale.scale2): return 2;
case (ASN1RealEncodingScale.scale3): return 3;
default:
throw new errors.ASN1Error("Impossible REAL encoding scale encountered.");
}
})(value[0] & 0b00001100);
let exponent;
let mantissa;
switch (value[0] & 0b00000011) {
case (0b00000000): {
if (value.length < 3)
throw new errors.ASN1TruncationError("Binary-encoded REAL truncated.");
exponent = decodeSignedBigEndianInteger(value.subarray(1, 2));
mantissa = decodeUnsignedBigEndianInteger(value.subarray(2));
break;
}
case (0b00000001): {
if (value.length < 4)
throw new errors.ASN1TruncationError("Binary-encoded REAL truncated.");
exponent = decodeSignedBigEndianInteger(value.subarray(1, 3));
mantissa = decodeUnsignedBigEndianInteger(value.subarray(3));
break;
}
case (0b00000010): {
if (value.length < 5)
throw new errors.ASN1TruncationError("Binary-encoded REAL truncated.");
exponent = decodeSignedBigEndianInteger(value.subarray(1, 4));
mantissa = decodeUnsignedBigEndianInteger(value.subarray(4));
break;
}
case (0b00000011): {
if (value.length < 3)
throw new errors.ASN1TruncationError("Binary-encoded REAL truncated.");
const exponentLength = value[1];
if (value.length < (3 + exponentLength)) {
throw new errors.ASN1TruncationError("Binary-encoded REAL truncated.");
}
exponent = decodeSignedBigEndianInteger(value.subarray(2, (2 + exponentLength)));
mantissa = decodeUnsignedBigEndianInteger(value.subarray((2 + exponentLength)));
break;
}
default:
throw new errors.ASN1Error("Impossible binary REAL exponent encoding encountered.");
}
return (sign * mantissa * Math.pow(2, scale) * Math.pow(base, exponent));
}
default:
throw new errors.ASN1Error("Impossible REAL format encountered.");
}
}