base32.c

// Base32 implementation
//
// Copyright 2010 Google Inc.
// Author: Markus Gutschke
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include <string.h>

#include "base32.h"

int base32_decode(const uint8_t *encoded, uint8_t *result, int buf_size) {
    int buffer = 0;
    int bits_left = 0;
    int count = 0;
    for (const uint8_t *ptr = encoded; count < buf_size && *ptr; ++ptr) {
        uint8_t ch = *ptr;
        if (ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n' || ch == '-') {
            continue;
        }
        buffer <<= 5;

        // Deal with commonly mistyped characters
        if (ch == '0') {
            ch = 'O';
        } else if (ch == '1') {
            ch = 'L';
        } else if (ch == '8') {
            ch = 'B';
        }

        // Look up one base32 digit
        if ((ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z')) {
            ch = (ch & 0x1F) - 1;
        } else if (ch >= '2' && ch <= '7') {
            ch -= '2' - 26;
        } else {
            return -1;
        }

        buffer |= ch;
        bits_left += 5;
        if (bits_left >= 8) {
            result[count++] = buffer >> (bits_left - 8);
            bits_left -= 8;
        }
    }
    if (count < buf_size) {
        result[count] = '\000';
    }
    return count;
}

int base32_encode(const uint8_t *data, int length, uint8_t *result, int buf_size) {
    if (length < 0 || length > (1 << 28)) {
        return -1;
    }
    int count = 0;
    if (length > 0) {
        uint32_t buffer = data[0];
        int next = 1;
        int bits_left = 8;
        while (count < buf_size && (bits_left > 0 || next < length)) {
            if (bits_left < 5) {
                if (next < length) {
                    buffer <<= 8;
                    buffer |= data[next++] & 0xFF;
                    bits_left += 8;
                } else {
                    int pad = 5 - bits_left;
                    buffer <<= pad;
                    bits_left += pad;
                }
            }
            int index = 0x1F & (buffer >> (bits_left - 5));
            bits_left -= 5;
            result[count++] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567"[index];
        }
    }
    if (count < buf_size) {
        result[count] = '\000';
    }
    return count;
}