/*
 * MIT License
 *
 * Copyright © 2019 Yibo Cai
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * Source: https://github.com/cyb70289/utf8
 */

#include <arm_neon.h>
#include <stdint.h>

#include "unicode.h"

#pragma GCC diagnostic ignored "-Woverflow"

static const uint8_t _first_len_tbl[] = {
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 3,
};

static const uint8_t _first_range_tbl[] = {
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 8, 8, 8,
};

static const uint8_t _range_min_tbl[] = {
	0x00, 0x80, 0x80, 0x80, 0xA0, 0x80, 0x90, 0x80,
	0xC2, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
};
static const uint8_t _range_max_tbl[] = {
	0x7F, 0xBF, 0xBF, 0xBF, 0xBF, 0x9F, 0xBF, 0x8F,
	0xF4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
};

static const uint8_t _range_adjust_tbl[] = {
	2, 3, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0,
	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0,
};

bool
utf8_validate_simd(const unsigned char *s, size_t len)
{
	if (len >= 32) {
		uint8x16_t prev_input = vdupq_n_u8(0);
		uint8x16_t prev_first_len = vdupq_n_u8(0);

		const uint8x16_t first_len_tbl = vld1q_u8(_first_len_tbl);
		const uint8x16_t first_range_tbl = vld1q_u8(_first_range_tbl);
		const uint8x16_t range_min_tbl = vld1q_u8(_range_min_tbl);
		const uint8x16_t range_max_tbl = vld1q_u8(_range_max_tbl);
		const uint8x16x2_t range_adjust_tbl = vld2q_u8(_range_adjust_tbl);

		const uint8x16_t const_1 = vdupq_n_u8(1);
		const uint8x16_t const_2 = vdupq_n_u8(2);
		const uint8x16_t const_e0 = vdupq_n_u8(0xE0);

		uint8x16_t error1 = vdupq_n_u8(0);
		uint8x16_t error2 = vdupq_n_u8(0);
		uint8x16_t error3 = vdupq_n_u8(0);
		uint8x16_t error4 = vdupq_n_u8(0);

		while (len >= 32) {
#if defined(__GNUC__) && !defined(__clang__) && (__GNUC__ < 8)
			/* GCC doesn't support vldq1_u8_x2 until version 8 */
			const uint8x16_t input_a = vld1q_u8(data);
			const uint8x16_t input_b = vld1q_u8(data + 16);
#else
			/* Forces a double load on Clang */
			const uint8x16x2_t input_pair = vld1q_u8_x2(s);
			const uint8x16_t input_a = input_pair.val[0];
			const uint8x16_t input_b = input_pair.val[1];
#endif

			const uint8x16_t high_nibbles_a = vshrq_n_u8(input_a, 4);
			const uint8x16_t high_nibbles_b = vshrq_n_u8(input_b, 4);

			const uint8x16_t first_len_a = vqtbl1q_u8(first_len_tbl,
			                                          high_nibbles_a);
			const uint8x16_t first_len_b = vqtbl1q_u8(first_len_tbl,
			                                          high_nibbles_b);

			uint8x16_t range_a = vqtbl1q_u8(first_range_tbl, high_nibbles_a);
			uint8x16_t range_b = vqtbl1q_u8(first_range_tbl, high_nibbles_b);

			range_a = vorrq_u8(range_a,
			                   vextq_u8(prev_first_len, first_len_a, 15));
			range_b = vorrq_u8(range_b, vextq_u8(first_len_a, first_len_b, 15));

			uint8x16_t tmp1_a, tmp2_a, tmp1_b, tmp2_b;
			tmp1_a = vextq_u8(prev_first_len, first_len_a, 14);
			tmp1_a = vqsubq_u8(tmp1_a, const_1);
			range_a = vorrq_u8(range_a, tmp1_a);

			tmp1_b = vextq_u8(first_len_a, first_len_b, 14);
			tmp1_b = vqsubq_u8(tmp1_b, const_1);
			range_b = vorrq_u8(range_b, tmp1_b);

			tmp2_a = vextq_u8(prev_first_len, first_len_a, 13);
			tmp2_a = vqsubq_u8(tmp2_a, const_2);
			range_a = vorrq_u8(range_a, tmp2_a);

			tmp2_b = vextq_u8(first_len_a, first_len_b, 13);
			tmp2_b = vqsubq_u8(tmp2_b, const_2);
			range_b = vorrq_u8(range_b, tmp2_b);

			uint8x16_t shift1_a = vextq_u8(prev_input, input_a, 15);
			uint8x16_t pos_a = vsubq_u8(shift1_a, const_e0);
			range_a = vaddq_u8(range_a, vqtbl2q_u8(range_adjust_tbl, pos_a));

			uint8x16_t shift1_b = vextq_u8(input_a, input_b, 15);
			uint8x16_t pos_b = vsubq_u8(shift1_b, const_e0);
			range_b = vaddq_u8(range_b, vqtbl2q_u8(range_adjust_tbl, pos_b));

			uint8x16_t minv_a = vqtbl1q_u8(range_min_tbl, range_a);
			uint8x16_t maxv_a = vqtbl1q_u8(range_max_tbl, range_a);

			uint8x16_t minv_b = vqtbl1q_u8(range_min_tbl, range_b);
			uint8x16_t maxv_b = vqtbl1q_u8(range_max_tbl, range_b);

			error1 = vorrq_u8(error1, vcltq_u8(input_a, minv_a));
			error2 = vorrq_u8(error2, vcgtq_u8(input_a, maxv_a));

			error3 = vorrq_u8(error3, vcltq_u8(input_b, minv_b));
			error4 = vorrq_u8(error4, vcgtq_u8(input_b, maxv_b));

			prev_input = input_b;
			prev_first_len = first_len_b;

			s += 32;
			len -= 32;
		}
		error1 = vorrq_u8(error1, error2);
		error1 = vorrq_u8(error1, error3);
		error1 = vorrq_u8(error1, error4);

		if (vmaxvq_u8(error1))
			return -1;

		uint32_t token4;
		vst1q_lane_u32(&token4, vreinterpretq_u32_u8(prev_input), 3);

		const int8_t *token = (const int8_t *)&token4;
		int lookahead = 0;
		if (token[3] > (int8_t)0xBF)
			lookahead = 1;
		else if (token[2] > (int8_t)0xBF)
			lookahead = 2;
		else if (token[1] > (int8_t)0xBF)
			lookahead = 3;

		s -= lookahead;
		len += lookahead;
	}

	return utf8_validate_off(s, len) == 0;
}