Fix miscellaneous lint warnings.

[wasi-libc.git] / libc-top-half / sources / arc4random.c

#include <assert.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <stdlib.h>

#define RNG_RESERVE_LEN 512

#define CHACHA20_KEYBYTES 32
#define CHACHA20_BLOCKBYTES 64

#define ROTL32(x, b) (uint32_t)(((x) << (b)) | ((x) >> (32 - (b))))

#define CHACHA20_QUARTERROUND(A, B, C, D) \
	A += B;                               \
	D = ROTL32(D ^ A, 16);                \
	C += D;                               \
	B = ROTL32(B ^ C, 12);                \
	A += B;                               \
	D = ROTL32(D ^ A, 8);                 \
	C += D;                               \
	B = ROTL32(B ^ C, 7)

static void CHACHA20_ROUNDS(uint32_t st[16])
{
	int i;

	for (i = 0; i < 20; i += 2) {
		CHACHA20_QUARTERROUND(st[0], st[4], st[8], st[12]);
		CHACHA20_QUARTERROUND(st[1], st[5], st[9], st[13]);
		CHACHA20_QUARTERROUND(st[2], st[6], st[10], st[14]);
		CHACHA20_QUARTERROUND(st[3], st[7], st[11], st[15]);
		CHACHA20_QUARTERROUND(st[0], st[5], st[10], st[15]);
		CHACHA20_QUARTERROUND(st[1], st[6], st[11], st[12]);
		CHACHA20_QUARTERROUND(st[2], st[7], st[8], st[13]);
		CHACHA20_QUARTERROUND(st[3], st[4], st[9], st[14]);
	}
}

static void chacha20_update(uint8_t out[CHACHA20_BLOCKBYTES], uint32_t st[16])
{
	uint32_t ks[16];
	int i;

	memcpy(ks, st, 4 * 16);
	CHACHA20_ROUNDS(st);
	for (i = 0; i < 16; i++) {
		ks[i] += st[i];
	}
	memcpy(out, ks, CHACHA20_BLOCKBYTES);
	st[12]++;
}

static void chacha20_init(uint32_t st[16], const uint8_t key[CHACHA20_KEYBYTES])
{
	static const uint32_t constants[4] = { 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574 };
	memcpy(&st[0], constants, 4 * 4);
	memcpy(&st[4], key, CHACHA20_KEYBYTES);
	memset(&st[12], 0, 4 * 4);
}

static int chacha20_rng(uint8_t* out, size_t len, uint8_t key[CHACHA20_KEYBYTES])
{
	uint32_t st[16];
	size_t off;

	chacha20_init(st, key);
	chacha20_update(&out[0], st);
	memcpy(key, out, CHACHA20_KEYBYTES);
	off = 0;
	while (len >= CHACHA20_BLOCKBYTES) {
		chacha20_update(&out[off], st);
		len -= CHACHA20_BLOCKBYTES;
		off += CHACHA20_BLOCKBYTES;
	}
	if (len > 0) {
		uint8_t tmp[CHACHA20_BLOCKBYTES];
		chacha20_update(tmp, st);
		memcpy(&out[off], tmp, len);
	}
	return 0;
}

struct rng_state {
	int initialized;
	size_t off;
	uint8_t key[CHACHA20_KEYBYTES];
	uint8_t reserve[RNG_RESERVE_LEN];
};

void arc4random_buf(void* buffer, size_t len)
{
	static _Thread_local struct rng_state rng_state;

	unsigned char* buffer_ = (unsigned char*)buffer;
	size_t off;
	size_t remaining;
	size_t partial;

	if (!rng_state.initialized) {
		if (getentropy(rng_state.key, sizeof rng_state.key) != 0) {
			assert(0);
		}
		rng_state.off = RNG_RESERVE_LEN;
		rng_state.initialized = 1;
	}
	off = 0;
	remaining = len;
	while (remaining > 0) {
		if (rng_state.off == RNG_RESERVE_LEN) {
			while (remaining >= RNG_RESERVE_LEN) {
				chacha20_rng(&buffer_[off], RNG_RESERVE_LEN, rng_state.key);
				off += RNG_RESERVE_LEN;
				remaining -= RNG_RESERVE_LEN;
			}
			if (remaining == 0) {
				break;
			}
			chacha20_rng(&rng_state.reserve[0], RNG_RESERVE_LEN, rng_state.key);
			rng_state.off = 0;
		}
		partial = RNG_RESERVE_LEN - rng_state.off;
		if (remaining < partial) {
			partial = remaining;
		}
		memcpy(&buffer_[off], &rng_state.reserve[rng_state.off], partial);
		memset(&rng_state.reserve[rng_state.off], 0, partial);
		rng_state.off += partial;
		remaining -= partial;
		off += partial;
	}
}

uint32_t arc4random(void)
{
	uint32_t v;

	arc4random_buf(&v, sizeof v);

	return v;
}

uint32_t arc4random_uniform(const uint32_t upper_bound)
{
	uint32_t min;
	uint32_t r;

	if (upper_bound < 2U) {
		return 0;
	}
	min = (1U + ~upper_bound) % upper_bound; /* = 2**32 mod upper_bound */
	do {
		r = arc4random();
	} while (r < min);
	/* r is now clamped to a set whose size mod upper_bound == 0
     * the worst case (2**31+1) requires 2 attempts on average */

	return r % upper_bound;
}