cjdns/util/VarInt.h

/* vim: set expandtab ts=4 sw=4: */
/*
 * You may redistribute this program and/or modify it under the terms of
 * the GNU General Public License as published by the Free Software Foundation,
 * either version 3 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, see <https://www.gnu.org/licenses/>.
 */
#ifndef VarInt_H
#define VarInt_H

#include "util/Bits.h"
#include "util/Gcc.h"

#include <stdint.h>

// Thank you Satoshi

struct VarInt_Iter {
    uint8_t* ptr;
    uint8_t* end;
    uint8_t* start;
};

static inline void VarInt_clone(struct VarInt_Iter* out, const struct VarInt_Iter* in)
{
    out->ptr = in->ptr;
    out->start = in->start;
    out->end = in->end;
}

static inline void VarInt_mk(struct VarInt_Iter* out, uint8_t* ptr, int length)
{
    out->ptr = ptr;
    out->end = ptr + length;
    out->start = ptr;
}

static inline void VarInt_toStart(struct VarInt_Iter* iter)
{
    iter->ptr = iter->start;
}

static inline void VarInt_toEnd(struct VarInt_Iter* iter)
{
    iter->ptr = iter->end;
}

static inline int VarInt_hasMore(struct VarInt_Iter* iter)
{
    return iter->end > iter->ptr;
}

static inline int VarInt_sizeOf(uint64_t val)
{
    return (!!(val >> 32)) * 4 + (!!(val >> 16)) * 2 + (!!((val + 3) >> 8)) + 1;
}

static inline int VarInt_pop(struct VarInt_Iter* iter, uint64_t* _out)
{
    uint64_t out = 0;
    uint8_t* bytes = iter->ptr;
    int len = iter->end - bytes;
    if (len < 9) {
        if (len < 5) {
            if (len < 3) {
                if (len < 1) { return -1; }
                if (*bytes >= 0xfd) { return -1; }
            } else if (*bytes >= 0xfe) { return -1; }
        } else if (*bytes >= 0xff) { return -1; }
    }
    switch (*bytes) {
        case 0xff:
            out |= *++bytes; out <<= 8;
            out |= *++bytes; out <<= 8;
            out |= *++bytes; out <<= 8;
            out |= *++bytes; out <<= 8;
            Gcc_FALLTHRU
        case 0xfe:
            out |= *++bytes; out <<= 8;
            out |= *++bytes; out <<= 8;
            Gcc_FALLTHRU
        case 0xfd:
            out |= *++bytes; out <<= 8;
            bytes++;
            Gcc_FALLTHRU
        default:
            out |= *bytes++;
    }
    iter->ptr = bytes;
    if (_out) { *_out = out; }
    return 0;
}

static inline int VarInt_push(struct VarInt_Iter* iter, uint64_t val)
{
    uint8_t* ptr = iter->ptr;
    int padding = ptr - iter->start;
    if (padding < 9) {
        if (padding < 5) {
            if (padding < 3) {
                if (padding < 1) { return -1; }
                if (val > 0xfc) { return -1; }
            } else if (val > 0xffff) { return -1; }
        } else if (val > 0xffffffff) { return -1; }
    }
    int i = VarInt_sizeOf(val);
    for (int j = 0; j < i; j++) { *--ptr = val & 0xff; val >>= 8; }
    switch (i) {
        case 8: *--ptr = 0xff; break;
        case 4: *--ptr = 0xfe; break;
        case 2: *--ptr = 0xfd; break;
    }
    iter->ptr = ptr;
    return 0;
}


#endif