Modular Exponentiation Calculator

            def modular_power(base: int, exponent: int, modulus: int) -> int:
    base, out = base % modulus, 1 % modulus
    while exponent:
        if exponent & 1: out = out * base % modulus
        base = base * base % modulus
        exponent >>= 1
    return out
assert modular_power(3, 13, 7) == 3
          

            #include <assert.h>
#include <stdint.h>
uint64_t modular_power(uint64_t a,uint64_t e,uint64_t m){uint64_t out=1%m;a%=m;while(e){if(e&1)out=out*a%m;a=a*a%m;e>>=1;}return out;}
int main(void){assert(modular_power(3,13,7)==3);}
          

            #include <cassert>
#include <cstdint>
std::uint64_t modular_power(std::uint64_t a,std::uint64_t e,std::uint64_t m){std::uint64_t out=1%m;a%=m;while(e){if(e&1)out=out*a%m;a=a*a%m;e>>=1;}return out;}
int main(){assert(modular_power(3,13,7)==3);}
          

x86-64 NASM · System V ABI · Linux · integer arguments in rdi, rsi and rdx

            ; uint64_t modular_power(uint64_t base, uint64_t exponent, uint64_t modulus)
global modular_power
section .text
modular_power:
    mov r8, rdx
    mov rax, rdi
    xor edx, edx
    div r8
    mov rdi, rdx
    mov eax, 1
    xor edx, edx
    div r8
    mov r9, rdx
.loop:
    test rsi, rsi
    jz .done
    test sil, 1
    jz .square
    mov rax, r9
    mul rdi
    div r8
    mov r9, rdx
.square:
    mov rax, rdi
    mul rdi
    div r8
    mov rdi, rdx
    shr rsi, 1
    jmp .loop
.done:
    mov rax, r9
    ret
          

            function result = modular_power(a, n, b)
    modulus = abs(round(b)); exponent = round(n);
    result = 1; base = mod(round(a), modulus);
    while exponent > 0
        if mod(exponent, 2) == 1, result = mod(result * base, modulus); end
        base = mod(base * base, modulus); exponent = floor(exponent / 2);
    end
end
          

            ClearAll[mwCalculate];
mwCalculate[a_Integer, n_Integer?NonNegative, b_Integer] /; b != 0 := PowerMod[a, n, Abs[b]];