/*
 * Copyright 2013 Google Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */
/*
 * Author: ncardwell@google.com (Neal Cardwell)
 *
 * Helpers to calculate IP, TCP, and UDP checksums.
 */

#include "checksum.h"

#include "assert.h"

/* Add bytes in buffer to a running checksum. Returns the new
 * intermediate checksum. Use ip_checksum_fold() to convert the
 * intermediate checksum to final form.
 */
static u64 ip_checksum_partial(const void *p, size_t len, u64 sum)
{
	/* Main loop: 32 bits at a time.
	 * We take advantage of intel's ability to do unaligned memory
	 * accesses with minimal additional cost. Other architectures
	 * probably want to be more careful here.
	 */
	const u32 *p32 = (const u32 *)(p);
	for (; len >= sizeof(*p32); len -= sizeof(*p32))
		sum += *p32++;

	/* Handle un-32bit-aligned trailing bytes */
	const u16 *p16 = (const u16 *)(p32);
	if (len >= 2) {
		sum += *p16++;
		len -= sizeof(*p16);
	}
	if (len > 0) {
		const u8 *p8 = (const u8 *)(p16);
		sum += ntohs(*p8 << 8);	/* RFC says pad last byte */
	}

	return sum;
}

static __be16 ip_checksum_fold(u64 sum)
{
	while (sum & ~0xffffffffULL)
		sum = (sum >> 32) + (sum & 0xffffffffULL);
	while (sum & 0xffff0000ULL)
		sum = (sum >> 16) + (sum & 0xffffULL);

	return ~sum;
}

static u64 tcp_udp_v4_header_checksum_partial(
	struct in_addr src_ip, struct in_addr dst_ip, u8 protocol, u16 len)
{
	/* The IPv4 pseudo-header is defined in RFC 793, Section 3.1. */
	struct ipv4_pseudo_header_t {
		/* We use a union here to avoid aliasing issues with gcc -O2 */
		union {
			struct header {
				struct in_addr src_ip;
				struct in_addr dst_ip;
				__u8 mbz;
				__u8 protocol;
				__be16 length;
			} __packed fields;
			u32 words[3];
		};
	};
	struct ipv4_pseudo_header_t pseudo_header;
	assert(sizeof(pseudo_header) == 12);

	/* Fill in the pseudo-header. */
	pseudo_header.fields.src_ip = src_ip;
	pseudo_header.fields.dst_ip = dst_ip;
	pseudo_header.fields.mbz = 0;
	pseudo_header.fields.protocol = protocol;
	pseudo_header.fields.length = htons(len);
	return ip_checksum_partial(&pseudo_header, sizeof(pseudo_header), 0);
}

__be16 tcp_udp_v4_checksum(struct in_addr src_ip, struct in_addr dst_ip,
			   u8 protocol, const void *payload, u16 len)
{
	u64 sum = tcp_udp_v4_header_checksum_partial(
		src_ip, dst_ip, protocol, len);
	sum = ip_checksum_partial(payload, len, sum);
	return ip_checksum_fold(sum);
}

/* Calculates and returns IPv4 header checksum. */
__be16 ipv4_checksum(void *ip_header, size_t ip_header_bytes)
{
	return ip_checksum_fold(
		ip_checksum_partial(ip_header, ip_header_bytes, 0));
}

static u64 tcp_udp_v6_header_checksum_partial(
	const struct in6_addr *src_ip,
	const struct in6_addr *dst_ip,
	u8 protocol, u32 len)
{
	/* The IPv6 pseudo-header is defined in RFC 2460, Section 8.1. */
	struct ipv6_pseudo_header_t {
		/* We use a union here to avoid aliasing issues with gcc -O2 */
		union {
			struct header {
				struct in6_addr src_ip;
				struct in6_addr dst_ip;
				__be32 length;
				__u8 mbz[3];
				__u8 next_header;
			} __packed fields;
			u32 words[10];
		};
	};
	struct ipv6_pseudo_header_t pseudo_header;
	assert(sizeof(pseudo_header) == 40);

	/* Fill in the pseudo-header. */
	pseudo_header.fields.src_ip = *src_ip;
	pseudo_header.fields.dst_ip = *dst_ip;
	pseudo_header.fields.length = htonl(len);
	memset(pseudo_header.fields.mbz, 0, sizeof(pseudo_header.fields.mbz));
	pseudo_header.fields.next_header = protocol;
	return ip_checksum_partial(&pseudo_header, sizeof(pseudo_header), 0);
}

__be16 tcp_udp_v6_checksum(const struct in6_addr *src_ip,
			   const struct in6_addr *dst_ip,
			   u8 protocol, const void *payload, u32 len)
{
	u64 sum = tcp_udp_v6_header_checksum_partial(
		src_ip, dst_ip, protocol, len);
	sum = ip_checksum_partial(payload, len, sum);
	return ip_checksum_fold(sum);
}

#define CRC32C(c, d) (c = (c>>8) ^ crc_c[(c^(d))&0xFF])

static u32 crc_c[256] = {
	0x00000000, 0xF26B8303, 0xE13B70F7, 0x1350F3F4,
	0xC79A971F, 0x35F1141C, 0x26A1E7E8, 0xD4CA64EB,
	0x8AD958CF, 0x78B2DBCC, 0x6BE22838, 0x9989AB3B,
	0x4D43CFD0, 0xBF284CD3, 0xAC78BF27, 0x5E133C24,
	0x105EC76F, 0xE235446C, 0xF165B798, 0x030E349B,
	0xD7C45070, 0x25AFD373, 0x36FF2087, 0xC494A384,
	0x9A879FA0, 0x68EC1CA3, 0x7BBCEF57, 0x89D76C54,
	0x5D1D08BF, 0xAF768BBC, 0xBC267848, 0x4E4DFB4B,
	0x20BD8EDE, 0xD2D60DDD, 0xC186FE29, 0x33ED7D2A,
	0xE72719C1, 0x154C9AC2, 0x061C6936, 0xF477EA35,
	0xAA64D611, 0x580F5512, 0x4B5FA6E6, 0xB93425E5,
	0x6DFE410E, 0x9F95C20D, 0x8CC531F9, 0x7EAEB2FA,
	0x30E349B1, 0xC288CAB2, 0xD1D83946, 0x23B3BA45,
	0xF779DEAE, 0x05125DAD, 0x1642AE59, 0xE4292D5A,
	0xBA3A117E, 0x4851927D, 0x5B016189, 0xA96AE28A,
	0x7DA08661, 0x8FCB0562, 0x9C9BF696, 0x6EF07595,
	0x417B1DBC, 0xB3109EBF, 0xA0406D4B, 0x522BEE48,
	0x86E18AA3, 0x748A09A0, 0x67DAFA54, 0x95B17957,
	0xCBA24573, 0x39C9C670, 0x2A993584, 0xD8F2B687,
	0x0C38D26C, 0xFE53516F, 0xED03A29B, 0x1F682198,
	0x5125DAD3, 0xA34E59D0, 0xB01EAA24, 0x42752927,
	0x96BF4DCC, 0x64D4CECF, 0x77843D3B, 0x85EFBE38,
	0xDBFC821C, 0x2997011F, 0x3AC7F2EB, 0xC8AC71E8,
	0x1C661503, 0xEE0D9600, 0xFD5D65F4, 0x0F36E6F7,
	0x61C69362, 0x93AD1061, 0x80FDE395, 0x72966096,
	0xA65C047D, 0x5437877E, 0x4767748A, 0xB50CF789,
	0xEB1FCBAD, 0x197448AE, 0x0A24BB5A, 0xF84F3859,
	0x2C855CB2, 0xDEEEDFB1, 0xCDBE2C45, 0x3FD5AF46,
	0x7198540D, 0x83F3D70E, 0x90A324FA, 0x62C8A7F9,
	0xB602C312, 0x44694011, 0x5739B3E5, 0xA55230E6,
	0xFB410CC2, 0x092A8FC1, 0x1A7A7C35, 0xE811FF36,
	0x3CDB9BDD, 0xCEB018DE, 0xDDE0EB2A, 0x2F8B6829,
	0x82F63B78, 0x709DB87B, 0x63CD4B8F, 0x91A6C88C,
	0x456CAC67, 0xB7072F64, 0xA457DC90, 0x563C5F93,
	0x082F63B7, 0xFA44E0B4, 0xE9141340, 0x1B7F9043,
	0xCFB5F4A8, 0x3DDE77AB, 0x2E8E845F, 0xDCE5075C,
	0x92A8FC17, 0x60C37F14, 0x73938CE0, 0x81F80FE3,
	0x55326B08, 0xA759E80B, 0xB4091BFF, 0x466298FC,
	0x1871A4D8, 0xEA1A27DB, 0xF94AD42F, 0x0B21572C,
	0xDFEB33C7, 0x2D80B0C4, 0x3ED04330, 0xCCBBC033,
	0xA24BB5A6, 0x502036A5, 0x4370C551, 0xB11B4652,
	0x65D122B9, 0x97BAA1BA, 0x84EA524E, 0x7681D14D,
	0x2892ED69, 0xDAF96E6A, 0xC9A99D9E, 0x3BC21E9D,
	0xEF087A76, 0x1D63F975, 0x0E330A81, 0xFC588982,
	0xB21572C9, 0x407EF1CA, 0x532E023E, 0xA145813D,
	0x758FE5D6, 0x87E466D5, 0x94B49521, 0x66DF1622,
	0x38CC2A06, 0xCAA7A905, 0xD9F75AF1, 0x2B9CD9F2,
	0xFF56BD19, 0x0D3D3E1A, 0x1E6DCDEE, 0xEC064EED,
	0xC38D26C4, 0x31E6A5C7, 0x22B65633, 0xD0DDD530,
	0x0417B1DB, 0xF67C32D8, 0xE52CC12C, 0x1747422F,
	0x49547E0B, 0xBB3FFD08, 0xA86F0EFC, 0x5A048DFF,
	0x8ECEE914, 0x7CA56A17, 0x6FF599E3, 0x9D9E1AE0,
	0xD3D3E1AB, 0x21B862A8, 0x32E8915C, 0xC083125F,
	0x144976B4, 0xE622F5B7, 0xF5720643, 0x07198540,
	0x590AB964, 0xAB613A67, 0xB831C993, 0x4A5A4A90,
	0x9E902E7B, 0x6CFBAD78, 0x7FAB5E8C, 0x8DC0DD8F,
	0xE330A81A, 0x115B2B19, 0x020BD8ED, 0xF0605BEE,
	0x24AA3F05, 0xD6C1BC06, 0xC5914FF2, 0x37FACCF1,
	0x69E9F0D5, 0x9B8273D6, 0x88D28022, 0x7AB90321,
	0xAE7367CA, 0x5C18E4C9, 0x4F48173D, 0xBD23943E,
	0xF36E6F75, 0x0105EC76, 0x12551F82, 0xE03E9C81,
	0x34F4F86A, 0xC69F7B69, 0xD5CF889D, 0x27A40B9E,
	0x79B737BA, 0x8BDCB4B9, 0x988C474D, 0x6AE7C44E,
	0xBE2DA0A5, 0x4C4623A6, 0x5F16D052, 0xAD7D5351
};

__be32 sctp_crc32c(const void *packet, u32 len)
{
	u32 i, crc32c;
	u8 byte0, byte1, byte2, byte3;
	const u8 *buf = (const u8 *)packet;

	crc32c = ~0;
	for (i = 0; i < len; i++)
		CRC32C(crc32c, buf[i]);
	crc32c = ~crc32c;
	byte0  = crc32c & 0xff;
	byte1  = (crc32c>>8) & 0xff;
	byte2  = (crc32c>>16) & 0xff;
	byte3  = (crc32c>>24) & 0xff;
	crc32c = ((byte0 << 24) | (byte1 << 16) | (byte2 << 8) | byte3);
	return htonl(crc32c);
}