#include <stdlib.h>
#include <string.h>

static bool is_big_endian(void)
{
	union
	{
		uint32_t i;
		char c[4];
	} bint = {0x01020304};

	return bint.c[0] == 1;
}

/* Decode an unsigned int LEB128 at buf into r, returning the nr of bytes read.
 */
inline size_t
decode_uint_leb(const uint8_t* buf, const uint8_t* buf_end, uint64_t* r)
{
	const uint8_t* p = buf;
	uint8_t shift = 0;
	uint64_t result = 0;
	uint8_t byte;

	do
	{
		if (p >= buf_end)
		{
			return 0;
		}
		byte = *p++;
		result |= ((uint64_t)(byte & 0x7f)) << shift;
		shift += 7;
	} while ((byte & 0x80) != 0);
	*r = result;
	return p - buf;
}

/* Decodes a string
 */
inline size_t decode_string(uint8_t str_len,
                            const uint8_t* buf,
                            const uint8_t* buf_end,
                            char* char_buf)
{
	// Return zero bytes read on buffer overflow
	if (buf_end - buf < str_len)
	{
		return 0;
	}
	const uint8_t* p = buf;
	for (int i = 0; i < str_len; i++)
	{
		char_buf[i] = *p++;
	}
	// Add the null terminator
	char_buf[str_len] = '\0';
	return str_len;
}

/* Decodes a double (8 bytes)
 */
inline size_t
decode_double(const uint8_t* buf, const uint8_t* buf_end, double* r)
{
	// Return zero bytes read on buffer overflow
	if (buf_end - buf < ((unsigned) sizeof(double)))
	{
		return 0;
	}
	if (is_big_endian())
	{
		uint8_t inverted[8] = {buf[7],
		                       buf[6],
		                       buf[5],
		                       buf[4],
		                       buf[3],
		                       buf[2],
		                       buf[1],
		                       buf[0]};
		memcpy(r, inverted, sizeof(double));
	}
	else
	{
		memcpy(r, buf, sizeof(double));
	}
	return sizeof(double);
}

/* Decodes a float (4 bytes)
 */
inline size_t decode_float(const uint8_t* buf, const uint8_t* buf_end, float* r)
{
	// Return zero bytes read on buffer overflow
	if (buf_end - buf < (unsigned) sizeof(float))
	{
		return 0;
	}
	if (is_big_endian())
	{
		uint8_t inverted[4] = {buf[3], buf[2], buf[1], buf[0]};
		memcpy(r, inverted, sizeof(float));
	}
	else
	{
		memcpy(r, buf, sizeof(float));
	}
	return sizeof(float);
}

/* Decodes a single byte
 */
inline size_t
decode_uint_8(const uint8_t* buf, const uint8_t* buf_end, uint8_t* r)
{
	// Return zero bytes read on buffer overflow
	if (buf_end - buf < (unsigned) sizeof(uint8_t))
	{
		return 0;
	}
	memcpy(r, buf, sizeof(uint8_t));
	return sizeof(uint8_t);
}

/* Decodes a 32 bit unsigned integer.
 */
inline size_t
decode_uint_32(const uint8_t* buf, const uint8_t* buf_end, uint32_t* r)
{
	// Return zero bytes read on buffer overflow
	if (buf_end - buf < (unsigned) sizeof(uint32_t))
	{
		return 0;
	}
	if (is_big_endian())
	{
		uint8_t inverted[4] = {buf[3], buf[2], buf[1], buf[0]};
		memcpy(r, inverted, sizeof(uint32_t));
	}
	else
	{
		memcpy(r, buf, sizeof(uint32_t));
	}
	return sizeof(uint32_t);
}