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