#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(uint64_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);
}