1 | //===-- Implementation of l64a --------------------------------------------===// |
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/l64a.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/libc_assert.h" |
14 | #include "src/__support/macros/config.h" |
15 | |
16 | #include <stdint.h> |
17 | |
18 | namespace LIBC_NAMESPACE_DECL { |
19 | |
20 | // the standard says to only use up to 6 characters. Null terminator is |
21 | // unnecessary, but we'll add it for ease-of-use. Also going from 48 -> 56 bits |
22 | // probably won't matter since it's likely 32-bit aligned anyways. |
23 | constexpr size_t MAX_BASE64_LENGTH = 6; |
24 | LIBC_THREAD_LOCAL char BASE64_BUFFER[MAX_BASE64_LENGTH + 1]; |
25 | |
26 | constexpr static char b64_int_to_char(uint32_t num) { |
27 | // from the standard: "The characters used to represent digits are '.' (dot) |
28 | // for 0, '/' for 1, '0' through '9' for [2,11], 'A' through 'Z' for [12,37], |
29 | // and 'a' through 'z' for [38,63]." |
30 | LIBC_ASSERT(num < 64); |
31 | if (num == 0) |
32 | return '.'; |
33 | if (num == 1) |
34 | return '/'; |
35 | if (num < 38) |
36 | return static_cast<char>( |
37 | internal::toupper(internal::int_to_b36_char(num - 2))); |
38 | |
39 | // this tolower is technically unnecessary, but it provides safety if we |
40 | // change the default behavior of int_to_b36_char. Also the compiler |
41 | // completely elides it so there's no performance penalty, see: |
42 | // https://godbolt.org/z/o5ennv7fc |
43 | return static_cast<char>( |
44 | internal::tolower(internal::int_to_b36_char(num - 2 - 26))); |
45 | } |
46 | |
47 | // This function takes a long and converts the low 32 bits of it into at most 6 |
48 | // characters. It's returned as a pointer to a static buffer. |
49 | LLVM_LIBC_FUNCTION(char *, l64a, (long value)) { |
50 | // static cast to uint32_t to get just the low 32 bits in a consistent way. |
51 | // The standard says negative values are undefined, so I'm just defining them |
52 | // to be treated as unsigned. |
53 | uint32_t cur_value = static_cast<uint32_t>(value); |
54 | for (size_t i = 0; i < MAX_BASE64_LENGTH; ++i) { |
55 | uint32_t cur_char = cur_value % 64; |
56 | BASE64_BUFFER[i] = b64_int_to_char(num: cur_char); |
57 | cur_value /= 64; |
58 | } |
59 | |
60 | BASE64_BUFFER[MAX_BASE64_LENGTH] = '\0'; // force null termination. |
61 | return BASE64_BUFFER; |
62 | } |
63 | |
64 | } // namespace LIBC_NAMESPACE_DECL |
65 | |