1//===-- Implementation of a64l --------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "src/stdlib/a64l.h"
10#include "hdr/types/size_t.h"
11#include "src/__support/common.h"
12#include "src/__support/ctype_utils.h"
13#include "src/__support/macros/config.h"
14
15#include <stdint.h>
16
17namespace LIBC_NAMESPACE_DECL {
18
19// I'm not sure this should go in ctype_utils since the specific ordering of
20// base64 is so very implementation specific, and also this set is unusual.
21// Returns -1 on any char without a specified value.
22constexpr static int32_t b64_char_to_int(char ch) {
23 // from the standard: "The characters used to represent digits are '.' (dot)
24 // for 0, '/' for 1, '0' through '9' for [2,11], 'A' through 'Z' for [12,37],
25 // and 'a' through 'z' for [38,63]."
26 if (ch == '.')
27 return 0;
28 if (ch == '/')
29 return 1;
30
31 // handle the case of an unspecified char.
32 if (!internal::isalnum(ch))
33 return -1;
34
35 bool is_lower = internal::islower(ch);
36 // add 2 to account for '.' and '/', then b36_char_to_int is case insensitive
37 // so add case sensitivity back.
38 return internal::b36_char_to_int(ch) + 2 + (is_lower ? 26 : 0);
39}
40
41// This function takes a base 64 string and writes it to the low 32 bits of a
42// long.
43// TODO: use LIBC_ADD_NULL_CHECKS for checking if the input is a null pointer.
44LLVM_LIBC_FUNCTION(long, a64l, (const char *s)) {
45 // the standard says to only use up to 6 characters.
46 constexpr size_t MAX_LENGTH = 6;
47 int32_t result = 0;
48
49 for (size_t i = 0; i < MAX_LENGTH && s[i] != '\0'; ++i) {
50 int32_t cur_val = b64_char_to_int(s[i]);
51 // The standard says what happens on an unspecified character is undefined,
52 // here we treat it as the end of the string.
53 if (cur_val == -1)
54 break;
55
56 // the first digit is the least significant, so for each subsequent digit we
57 // shift it more. 6 bits since 2^6 = 64
58 result += (cur_val << (6 * i));
59 }
60
61 // standard says to sign extend from 32 bits.
62 return static_cast<long>(result);
63}
64
65} // namespace LIBC_NAMESPACE_DECL
66

source code of libc/src/stdlib/a64l.cpp