yggm/libs/fprime.cuh

#ifndef __FPRIME_CUH
#define __FPRIME_CUH
#include <stdint.h>
#include <stddef.h>
#include <string.h>
#ifndef COMPACT_DISABLE_ED25519
#ifdef FULL_C25519_CODE
__device__ const uint8_t fprime_zero[FPRIME_SIZE] = { 0 };
__device__ const uint8_t fprime_one[FPRIME_SIZE] = { 1 };
#endif
#define FPRIME_SIZE  32
__device__ void raw_add(uint8_t* x, const uint8_t* p) {
    uint16_t c = 0;
    for (int i = 0; i < FPRIME_SIZE; i++) {
        c += ((uint16_t)x[i]) + ((uint16_t)p[i]);
        x[i] = (uint8_t)c;
        c >>= 8;
    }
}
__device__ void fprime_select(uint8_t* dst, const uint8_t* zero, const uint8_t* one, uint8_t condition) {
    const uint8_t mask = -condition;
    for (int i = 0; i < FPRIME_SIZE; i++)
        dst[i] = zero[i] ^ (mask & (one[i] ^ zero[i]));
}
__device__ void raw_try_sub(uint8_t* x, const uint8_t* p)
{
    uint8_t minusp[FPRIME_SIZE];
    uint16_t c = 0;
    for (int i = 0; i < FPRIME_SIZE; i++) {
        c = ((uint16_t)x[i]) - ((uint16_t)p[i]) - c;
        minusp[i] = (uint8_t)c;
        c = (c >> 8) & 1;
    }
    fprime_select(x, minusp, x, c);
}
__device__ int prime_msb(const uint8_t* p) {
    int i;
    uint8_t x;
    for (i = FPRIME_SIZE - 1; i >= 0; i--) {
        if (p[i])
            break;
    }
    x = p[i];
    i <<= 3;
    while (x) {
        x >>= 1;
        i++;
    }
    return i - 1;
}
__device__ void shift_n_bits(uint8_t* x, int n) {
    uint16_t c = 0;
    for (int i = 0; i < FPRIME_SIZE; i++) {
        c |= ((uint16_t)x[i]) << n;
        x[i] = (uint8_t)c;
        c >>= 8;
    }
}
#ifdef FULL_C25519_CODE
__device__ void fprime_load(uint8_t* x, uint32_t c)
{
    unsigned int i;
    for (i = 0; i < sizeof(c); i++) {
        x[i] = (uint8_t)c;
        c >>= 8;
    }
    for (; i < FPRIME_SIZE; i++)
        x[i] = 0;
}
#endif
__device__ inline int min_int(int a, int b) {
    return a < b ? a : b;
}
__device__ void fprime_from_bytes(uint8_t* n, const uint8_t* x, size_t len, const uint8_t* modulus) {
    const int preload_total = min_int(prime_msb(modulus) - 1, (int)(len << 3));
    const int preload_bytes = preload_total >> 3;
    const int preload_bits = preload_total & 7;
    const int rbits = (len << 3) - preload_total;
    memset(n, 0, FPRIME_SIZE);
    for (int i = 0; i < preload_bytes; i++)
        n[i] = x[len - preload_bytes + i];
    if (preload_bits) {
        shift_n_bits(n, preload_bits);
        n[0] |= x[len - preload_bytes - 1] >> (8 - preload_bits);
    }
    for (int i = rbits - 1; i >= 0; i--) {
        const uint8_t bit = (x[i >> 3] >> (i & 7)) & 1;
        shift_n_bits(n, 1);
        n[0] |= bit;
        raw_try_sub(n, modulus);
    }
}
#ifdef FULL_C25519_CODE
__device__ void fprime_normalize(uint8_t* x, const uint8_t* modulus) {
    uint8_t n[FPRIME_SIZE];
    fprime_from_bytes(n, x, FPRIME_SIZE, modulus);
    fprime_copy(x, n);
}
__device__ uint8_t fprime_eq(const uint8_t* x, const uint8_t* y) {
    uint8_t sum = 0;
    for (int i = 0; i < FPRIME_SIZE; i++)
        sum |= x[i] ^ y[i];
    sum |= (sum >> 4);
    sum |= (sum >> 2);
    sum |= (sum >> 1);
    return (sum ^ 1) & 1;
}
#endif
__device__ void fprime_add(uint8_t* r, const uint8_t* a, const uint8_t* modulus) {
    raw_add(r, a);
    raw_try_sub(r, modulus);
}
#ifdef FULL_C25519_CODE
__device__ void fprime_sub(uint8_t* r, const uint8_t* a, const uint8_t* modulus) {
    raw_add(r, modulus);
    raw_try_sub(r, a);
    raw_try_sub(r, modulus);
}
#endif
__device__ inline void fprime_copy(uint8_t* x, const uint8_t* a) {
    memcpy(x, a, FPRIME_SIZE);
}
__device__ void fprime_mul(uint8_t* r, const uint8_t* a, const uint8_t* b, const uint8_t* modulus) {
    memset(r, 0, FPRIME_SIZE);
    for (int i = prime_msb(modulus); i >= 0; i--) {
        const uint8_t bit = (b[i >> 3] >> (i & 7)) & 1;
        uint8_t plusa[FPRIME_SIZE];
        shift_n_bits(r, 1);
        raw_try_sub(r, modulus);
        fprime_copy(plusa, r);
        fprime_add(plusa, a, modulus);
        fprime_select(r, r, plusa, bit);
    }
}
#ifdef FULL_C25519_CODE
__device__ void fprime_inv(uint8_t* r, const uint8_t* a, const uint8_t* modulus) {
    uint8_t pm2[FPRIME_SIZE];
    uint16_t c = 2;
    fprime_copy(pm2, modulus);
    for (int i = 0; i < FPRIME_SIZE; i++) {
        c = modulus[i] - c;
        pm2[i] = (uint8_t)c;
        c >>= 8;
    }
    fprime_load(r, 1);
    for (int i = prime_msb(modulus); i >= 0; i--) {
        uint8_t r2[FPRIME_SIZE];
        fprime_mul(r2, r, r, modulus);
        if ((pm2[i >> 3] >> (i & 7)) & 1)
            fprime_mul(r, r2, a, modulus);
        else
            fprime_copy(r, r2);
    }
}
#endif
#endif
#endif