Int128

export type BrandedInt128 = bigint & {
  readonly [brand]: "Int128"
}

import * as Int128 from '@voltaire/primitives/Int128';

// Create from various sources
const a = Int128(-42n);
const b = Int128("0xffffffffffffffffffffffffffffffff"); // -1
const c = Int128(-100);

// Arithmetic (truncate toward zero)
Int128.dividedBy(-10n, 3n); // -3n (not -4)
Int128.modulo(-10n, 3n);     // -1n (sign follows dividend)

// Signed comparison
Int128.lessThan(-1n, 0n);    // true
Int128.greaterThan(0n, -1n); // true

// Bitwise (two's complement)
Int128.shiftRight(-256n, 1); // -128n (arithmetic shift, sign preserved)
Int128.bitwiseAnd(-1n, 0xffn); // 0xffn

// Two's complement encoding
Int128.toHex(-1n); // "0xffffffffffffffffffffffffffffffff"

// -1 is all bits set
Int128.toHex(-1n);
// "0xffffffffffffffffffffffffffffffff"

// MIN has high bit set
Int128.toHex(Int128.MIN);
// "0x80000000000000000000000000000000"

// MAX is 0x7f...
Int128.toHex(Int128.MAX);
// "0x7fffffffffffffffffffffffffffffff"

Int128.dividedBy(-10n, 3n);  // -3n (not -4n)
Int128.dividedBy(10n, -3n);  // -3n (not -4n)

// Modulo sign follows dividend
Int128.modulo(-10n, 3n);   // -1n (not 2n)
Int128.modulo(10n, -3n);   // 1n (not -2n)

// Property: a = (a/b)*b + (a%b)

Int128.shiftRight(-256n, 1); // -128n (sign preserved)
Int128.shiftRight(256n, 1);  // 128n
Int128.shiftRight(-1n, 8);   // -1n (all bits remain 1)

// MIN / -1 overflows (abs(MIN) doesn't fit)
Int128.dividedBy(Int128.MIN, -1n); // throws

// abs(MIN) overflows
Int128.abs(Int128.MIN); // throws

// negate(MIN) wraps
Int128.negate(Int128.MIN); // MIN (wraps around)

// Overflow wraps
Int128.plus(Int128.MAX, 1n); // MIN
Int128.minus(Int128.MIN, 1n); // MAX

Int128.MIN     // -2^127
Int128.MAX     // 2^127-1
Int128.ZERO    // 0n
Int128.ONE     // 1n
Int128.NEG_ONE // -1n
Int128.SIZE    // 16 (bytes)
Int128.BITS    // 128
Int128.MODULO  // 2^128