Zig 0.17.0-dev (Split by item)

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modularInverse

Modular inversion: computes a^(-1) mod p Requires gcd(a,p) = 1. The result is normalized to the range [0, p).

ml_dsa.modularInverse

fn modularInverse(comptime T: type, comptime a: T, comptime p: T) T

File

lib/std/crypto/ml_dsa.zig:3412

Code

fn modularInverse(comptime T: type, comptime a: T, comptime p: T) T {
    // Use a signed type for EEA computation
    const type_info = @typeInfo(T);
    const SignedT = if (type_info == .int and type_info.int.signedness == .unsigned)
        @Int(.signed, type_info.int.bits)
    else
        T;

    const a_signed = @as(SignedT, @intCast(a));
    const p_signed = @as(SignedT, @intCast(p));

    const r = extendedEuclidean(SignedT, a_signed, p_signed);
    assert(r.gcd == 1);

    // Normalize result to [0, p)
    var result = r.x;
    while (result < 0) {
        result += p_signed;
    }

    return @intCast(result);
}