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base64: use a less complicated validity check in the decode loop Checking each of the four input chars for validity generates horrible machine code with many comparisons and conditional jumps. We can reduce this to just one comparison and one conditional jump by making assumptions about what invalid inputs look like (i.e., 0xff). Suggested by Timo Sirainen. Signed-off-by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
author Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
date Wed, 29 May 2019 10:58:19 -0400
parents 12be3c54727b
children b7e409c72ad8
line wrap: on
line source

/*
 * Copyright (c) 2019 Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
 *
 * 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.
 */

#include <jeffpc/base64.h>

static const char b64_encode_table[64] =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	"abcdefghijklmnopqrstuvwxyz"
	"0123456789+/";

static const char b64url_encode_table[64] =
	"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
	"abcdefghijklmnopqrstuvwxyz"
	"0123456789-_";

#define INV	0xff
static const uint8_t b64_decode_table[256] = {
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x00..0x07 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x08..0x0f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x10..0x17 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x18..0x1f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x20..0x27 */
	 INV,  INV,  INV, 0x3e,  INV,  INV,  INV, 0x3f, /* 0x28..0x2f */
	0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, /* 0x30..0x37 */
	0x3c, 0x3d,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x38..0x3f */
	 INV, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, /* 0x40..0x47 */
	0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, /* 0x48..0x4f */
	0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, /* 0x50..0x57 */
	0x17, 0x18, 0x19,  INV,  INV,  INV,  INV,  INV, /* 0x58..0x5f */
	 INV, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, /* 0x60..0x67 */
	0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, /* 0x68..0x6f */
	0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, /* 0x70..0x77 */
	0x31, 0x32, 0x33,  INV,  INV,  INV,  INV,  INV, /* 0x78..0x7f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x80..0x87 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x88..0x8f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x90..0x97 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x98..0x9f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xa0..0xa7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xa8..0xaf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xb0..0xb7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xb8..0xbf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xc0..0xc7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xc8..0xcf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xd0..0xd7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xd8..0xdf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xe0..0xe7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xe8..0xef */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xf0..0xf7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xf8..0xff */
};

static const uint8_t b64url_decode_table[256] = {
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x00..0x07 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x08..0x0f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x10..0x17 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x18..0x1f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x20..0x27 */
	 INV,  INV,  INV,  INV,  INV, 0x3e,  INV,  INV, /* 0x28..0x2f */
	0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, /* 0x30..0x37 */
	0x3c, 0x3d,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x38..0x3f */
	 INV, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, /* 0x40..0x47 */
	0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, /* 0x48..0x4f */
	0x0f, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, /* 0x50..0x57 */
	0x17, 0x18, 0x19,  INV,  INV,  INV,  INV, 0x3f, /* 0x58..0x5f */
	 INV, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20, /* 0x60..0x67 */
	0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, /* 0x68..0x6f */
	0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, 0x30, /* 0x70..0x77 */
	0x31, 0x32, 0x33,  INV,  INV,  INV,  INV,  INV, /* 0x78..0x7f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x80..0x87 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x88..0x8f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x90..0x97 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0x98..0x9f */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xa0..0xa7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xa8..0xaf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xb0..0xb7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xb8..0xbf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xc0..0xc7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xc8..0xcf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xd0..0xd7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xd8..0xdf */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xe0..0xe7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xe8..0xef */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xf0..0xf7 */
	 INV,  INV,  INV,  INV,  INV,  INV,  INV,  INV, /* 0xf8..0xff */
};

__attribute__((always_inline))
static inline void __b64_encode(char *out, const void *_in, size_t inlen,
				const char *table)
{
	const uint8_t *in = _in;
	const size_t groups = inlen / 3;
	uint32_t v;
	size_t i;

	for (i = 0; i < groups; i++) {
		const size_t iidx = i * 3;
		const size_t oidx = i * 4;

		v =  in[iidx] << 16;
		v |= in[iidx + 1] << 8;
		v |= in[iidx + 2];

		out[oidx + 0] = table[(v >> 18) & 0x3f];
		out[oidx + 1] = table[(v >> 12) & 0x3f];
		out[oidx + 2] = table[(v >> 6) & 0x3f];
		out[oidx + 3] = table[(v >> 0) & 0x3f];
	}

	switch (inlen % 3) {
		case 0:
			/* nothing left - nul terminate */
			out[i * 4] = '\0';
			break;
		case 1:
			/* 1 byte left - encoded it & pad with == */
			v = in[i * 3] << 4;

			out[i * 4]     = table[(v >> 6) & 0x3f];
			out[i * 4 + 1] = table[(v >> 0) & 0x3f];
			out[i * 4 + 2] = '=';
			out[i * 4 + 3] = '=';
			out[i * 4 + 4] = '\0';
			break;
		case 2:
			/* 2 bytes left - encoded them & pad with = */
			v =  in[i * 3] << 8;
			v |= in[i * 3 + 1];

			out[i * 4]     = table[(v >> 12) & 0x3f];
			out[i * 4 + 1] = table[(v >> 6) & 0x3f];
			out[i * 4 + 2] = table[(v >> 0) & 0x3f];
			out[i * 4 + 3] = '=';
			out[i * 4 + 4] = '\0';
			break;
	}
}

void base64_encode(char *out, const void *in, size_t inlen)
{
	__b64_encode(out, in, inlen, b64_encode_table);
}

void base64url_encode(char *out, const void *in, size_t inlen)
{
	__b64_encode(out, in, inlen, b64url_encode_table);
}

__attribute__((always_inline))
static inline ssize_t __b64_decode(void *_out, const char *_in, size_t inlen,
				   const uint8_t *table)
{
	const uint8_t *in = (const uint8_t *) _in;
	uint8_t *out = _out;
	size_t groups;
	size_t i;

	if (inlen % 4)
		return -1;

	groups = inlen / 4;
	if (in[inlen - 1] == '=')
		groups--; /* last group has padding */

	for (i = 0; i < groups; i++) {
		const uint8_t a = table[in[(i * 4) + 0]];
		const uint8_t b = table[in[(i * 4) + 1]];
		const uint8_t c = table[in[(i * 4) + 2]];
		const uint8_t d = table[in[(i * 4) + 3]];
		uint32_t v;

		/*
		 * If any one of the four chars in this group is INV, error
		 * out.
		 *
		 * Optimization: Since no valid char translates to a value
		 * with with 0x40 or 0x80 set, the only way to get 0xff out
		 * is if one of the four values was 0xff - aka. INV.
		 */
		if ((a | b | c | d) == INV)
			return -1;

		v = (a << 18) | (b << 12) | (c << 6) | d;

		out[(i * 3) + 0] = (v >> 16) & 0xff;
		out[(i * 3) + 1] = (v >> 8) & 0xff;
		out[(i * 3) + 2] = (v >> 0) & 0xff;
	}

	if ((in[inlen - 2] == '=') && (in[inlen - 1] == '=')) {
		/* two pad chars, 1 byte of output left */
		const uint8_t a = table[in[inlen - 4]];
		const uint8_t b = table[in[inlen - 3]];
		uint32_t v;

		if ((a == INV) || (b == INV))
			return -1;

		v = (a << 2) | (b >> 4);

		out[(groups * 3) + 0] = v & 0xff;

		return (groups * 3) + 1;
	} else if (in[inlen - 1] == '=') {
		/* one pad char, 2 bytes of output left */
		const uint8_t a = table[in[inlen - 4]];
		const uint8_t b = table[in[inlen - 3]];
		const uint8_t c = table[in[inlen - 2]];
		uint32_t v;

		if ((a == INV) || (b == INV) || (c == INV))
			return -1;

		v = (a << 10) | (b << 4) | (c >> 2);

		out[(groups * 3) + 0] = (v >> 8) & 0xff;
		out[(groups * 3) + 1] = (v >> 0) & 0xff;

		return (groups * 3) + 2;
	} else {
		/* zero pad chars, nothing to do */
		return (groups * 3);
	}
}

ssize_t base64_decode(void *out, const char *in, size_t inlen)
{
	return __b64_decode(out, in, inlen, b64_decode_table);
}

ssize_t base64url_decode(void *out, const char *in, size_t inlen)
{
	return __b64_decode(out, in, inlen, b64url_decode_table);
}