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 | |
17 | namespace 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. |
22 | constexpr 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. |
44 | LLVM_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 | |