// The ChaCha stream cipher used for pseudorandom number generation

#pragma once
/*
chacha-merged.c version 20080118
D. J. Bernstein
Public domain.
*/

/* $OpenBSD: chacha_private.h,v 1.3 2022/02/28 21:56:29 dtucker Exp $ */
/* Tomo: chacha.h,v 1.0 2024/11/03 Bruce Hill */

typedef unsigned char u8;
typedef unsigned int u32;

typedef struct {
    u32 input[16]; /* could be compressed */
} chacha_ctx;

#define KEYSZ 32
#define IVSZ 8

#define U8C(v) (v##U)
#define U32C(v) (v##U)

#define U8V(v) ((u8)(v) & U8C(0xFF))
#define U32V(v) ((u32)(v) & U32C(0xFFFFFFFF))

#define ROTL32(v, n) (U32V((v) << (n)) | ((v) >> (32 - (n))))

#define U8TO32_LITTLE(p) (((u32)((p)[0])) | ((u32)((p)[1]) << 8) | ((u32)((p)[2]) << 16) | ((u32)((p)[3]) << 24))

#define U32TO8_LITTLE(p, v)                                                                                            \
    do {                                                                                                               \
        (p)[0] = U8V((v));                                                                                             \
        (p)[1] = U8V((v) >> 8);                                                                                        \
        (p)[2] = U8V((v) >> 16);                                                                                       \
        (p)[3] = U8V((v) >> 24);                                                                                       \
    } while (0)

#define ROTATE(v, c) (ROTL32(v, c))
#define XOR(v, w) ((v) ^ (w))
#define PLUS(v, w) (U32V((v) + (w)))
#define PLUSONE(v) (PLUS((v), 1))

#define QUARTERROUND(a, b, c, d)                                                                                       \
    a = PLUS(a, b);                                                                                                    \
    d = ROTATE(XOR(d, a), 16);                                                                                         \
    c = PLUS(c, d);                                                                                                    \
    b = ROTATE(XOR(b, c), 12);                                                                                         \
    a = PLUS(a, b);                                                                                                    \
    d = ROTATE(XOR(d, a), 8);                                                                                          \
    c = PLUS(c, d);                                                                                                    \
    b = ROTATE(XOR(b, c), 7);

static const char sigma[16] = "expand 32-byte k";

static void chacha_keysetup(chacha_ctx *chacha, const u8 *k) {
    chacha->input[0] = U8TO32_LITTLE(sigma + 0);
    chacha->input[1] = U8TO32_LITTLE(sigma + 4);
    chacha->input[2] = U8TO32_LITTLE(sigma + 8);
    chacha->input[3] = U8TO32_LITTLE(sigma + 12);
    chacha->input[4] = U8TO32_LITTLE(k + 0);
    chacha->input[5] = U8TO32_LITTLE(k + 4);
    chacha->input[6] = U8TO32_LITTLE(k + 8);
    chacha->input[7] = U8TO32_LITTLE(k + 12);
    chacha->input[8] = U8TO32_LITTLE(k + 16);
    chacha->input[9] = U8TO32_LITTLE(k + 20);
    chacha->input[10] = U8TO32_LITTLE(k + 24);
    chacha->input[11] = U8TO32_LITTLE(k + 28);
}

static void chacha_ivsetup(chacha_ctx *chacha, const u8 *iv) {
    chacha->input[12] = 0;
    chacha->input[13] = 0;
    chacha->input[14] = U8TO32_LITTLE(iv + 0);
    chacha->input[15] = U8TO32_LITTLE(iv + 4);
}

static void chacha_encrypt_bytes(chacha_ctx *chacha, const u8 *m, u8 *c, u32 bytes) {
    u32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
    u32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
    u8 *ctarget = (u8 *)0;
    u8 tmp[64];
    unsigned int i;

    if (!bytes) return;

    j0 = chacha->input[0];
    j1 = chacha->input[1];
    j2 = chacha->input[2];
    j3 = chacha->input[3];
    j4 = chacha->input[4];
    j5 = chacha->input[5];
    j6 = chacha->input[6];
    j7 = chacha->input[7];
    j8 = chacha->input[8];
    j9 = chacha->input[9];
    j10 = chacha->input[10];
    j11 = chacha->input[11];
    j12 = chacha->input[12];
    j13 = chacha->input[13];
    j14 = chacha->input[14];
    j15 = chacha->input[15];

    for (;;) {
        if (bytes < 64) {
            for (i = 0; i < bytes; ++i)
                tmp[i] = m[i];
            m = tmp;
            ctarget = c;
            c = tmp;
        }
        x0 = j0;
        x1 = j1;
        x2 = j2;
        x3 = j3;
        x4 = j4;
        x5 = j5;
        x6 = j6;
        x7 = j7;
        x8 = j8;
        x9 = j9;
        x10 = j10;
        x11 = j11;
        x12 = j12;
        x13 = j13;
        x14 = j14;
        x15 = j15;
        for (i = 20; i > 0; i -= 2) {
            QUARTERROUND(x0, x4, x8, x12)
            QUARTERROUND(x1, x5, x9, x13)
            QUARTERROUND(x2, x6, x10, x14)
            QUARTERROUND(x3, x7, x11, x15)
            QUARTERROUND(x0, x5, x10, x15)
            QUARTERROUND(x1, x6, x11, x12)
            QUARTERROUND(x2, x7, x8, x13)
            QUARTERROUND(x3, x4, x9, x14)
        }
        x0 = PLUS(x0, j0);
        x1 = PLUS(x1, j1);
        x2 = PLUS(x2, j2);
        x3 = PLUS(x3, j3);
        x4 = PLUS(x4, j4);
        x5 = PLUS(x5, j5);
        x6 = PLUS(x6, j6);
        x7 = PLUS(x7, j7);
        x8 = PLUS(x8, j8);
        x9 = PLUS(x9, j9);
        x10 = PLUS(x10, j10);
        x11 = PLUS(x11, j11);
        x12 = PLUS(x12, j12);
        x13 = PLUS(x13, j13);
        x14 = PLUS(x14, j14);
        x15 = PLUS(x15, j15);

        j12 = PLUSONE(j12);
        if (!j12) {
            j13 = PLUSONE(j13);
            /* stopping at 2^70 bytes per nonce is user's responsibility */
        }

        U32TO8_LITTLE(c + 0, x0);
        U32TO8_LITTLE(c + 4, x1);
        U32TO8_LITTLE(c + 8, x2);
        U32TO8_LITTLE(c + 12, x3);
        U32TO8_LITTLE(c + 16, x4);
        U32TO8_LITTLE(c + 20, x5);
        U32TO8_LITTLE(c + 24, x6);
        U32TO8_LITTLE(c + 28, x7);
        U32TO8_LITTLE(c + 32, x8);
        U32TO8_LITTLE(c + 36, x9);
        U32TO8_LITTLE(c + 40, x10);
        U32TO8_LITTLE(c + 44, x11);
        U32TO8_LITTLE(c + 48, x12);
        U32TO8_LITTLE(c + 52, x13);
        U32TO8_LITTLE(c + 56, x14);
        U32TO8_LITTLE(c + 60, x15);

        if (bytes <= 64) {
            if (bytes < 64) {
                for (i = 0; i < bytes; ++i)
                    ctarget[i] = c[i];
            }
            chacha->input[12] = j12;
            chacha->input[13] = j13;
            return;
        }
        bytes -= 64;
        c += 64;
    }
}