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modularPow

Modular exponentiation: computes a^s mod p using square-and-multiply algorithm.

ml_kem.modularPow

fn modularPow(comptime T: type, comptime a: T, s: T, comptime p: T) T

File

lib/std/crypto/ml_kem.zig:1817

Code

fn modularPow(comptime T: type, comptime a: T, s: T, comptime p: T) T {
    const type_info = @typeInfo(T);
    const bits = type_info.int.bits;
    const WideT = @Int(.unsigned, bits * 2);

    var ret: T = 1;
    var base: T = a;
    var exp = s;

    while (exp > 0) {
        if (exp & 1 == 1) {
            ret = @intCast((@as(WideT, ret) * @as(WideT, base)) % p);
        }
        base = @intCast((@as(WideT, base) * @as(WideT, base)) % p);
        exp >>= 1;
    }

    return ret;
}