28 lines
817 B
JavaScript

import JSBI from "jsbi";
export function interpretAsSignedType(n) {
// see https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/wire_format_lite.h#L857-L876
// however, this is a simpler equivalent formula
const isEven = JSBI.equal(JSBI.bitwiseAnd(n, JSBI.BigInt(1)), JSBI.BigInt(0));
if (isEven) {
return JSBI.divide(n, JSBI.BigInt(2));
} else {
return JSBI.multiply(
JSBI.BigInt(-1),
JSBI.divide(JSBI.add(n, JSBI.BigInt(1)), JSBI.BigInt(2))
);
}
}
export function interpretAsTwosComplement(n, bits) {
const isTwosComplement = JSBI.equal(
JSBI.signedRightShift(n, JSBI.BigInt(bits - 1)),
JSBI.BigInt(1)
);
if (isTwosComplement) {
return JSBI.subtract(n, JSBI.leftShift(JSBI.BigInt(1), JSBI.BigInt(bits)));
} else {
return n;
}
}