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
18namespace 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.
23constexpr size_t MAX_BASE64_LENGTH = 6;
24LIBC_THREAD_LOCAL char BASE64_BUFFER[MAX_BASE64_LENGTH + 1];
25
26constexpr 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.
49LLVM_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

source code of libc/src/stdlib/l64a.cpp