[libc++][C++17] Elementary string conversions for integral types
Summary: Major QoI considerations: - The facility is backported to C++14, same as libstdc++. - Efforts have been made to minimize the header dependencies. - The design is friendly to the uses of MSVC intrinsics (`__emulu`, `_umul128`, `_BitScanForward`, `_BitScanForward64`) but not implemented; future contributions are welcome. Thanks to Milo Yip for contributing the implementation of `__u64toa` and `__u32toa`. References: https://wg21.link/p0067r5 https://wg21.link/p0682r1 Reviewers: mclow.lists, EricWF Reviewed By: mclow.lists Subscribers: ldionne, Quuxplusone, christof, mgorny, cfe-commits Differential Revision: https://reviews.llvm.org/D41458 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@338479 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Zhihao Yuan
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src/charconv.cpp
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233
src/charconv.cpp
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//===------------------------- charconv.cpp -------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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#include "charconv"
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#include <string.h>
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_LIBCPP_BEGIN_NAMESPACE_STD
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namespace __itoa
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{
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static constexpr char cDigitsLut[200] = {
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'0', '0', '0', '1', '0', '2', '0', '3', '0', '4', '0', '5', '0', '6', '0',
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'7', '0', '8', '0', '9', '1', '0', '1', '1', '1', '2', '1', '3', '1', '4',
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'1', '5', '1', '6', '1', '7', '1', '8', '1', '9', '2', '0', '2', '1', '2',
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'2', '2', '3', '2', '4', '2', '5', '2', '6', '2', '7', '2', '8', '2', '9',
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'3', '0', '3', '1', '3', '2', '3', '3', '3', '4', '3', '5', '3', '6', '3',
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'7', '3', '8', '3', '9', '4', '0', '4', '1', '4', '2', '4', '3', '4', '4',
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'4', '5', '4', '6', '4', '7', '4', '8', '4', '9', '5', '0', '5', '1', '5',
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'2', '5', '3', '5', '4', '5', '5', '5', '6', '5', '7', '5', '8', '5', '9',
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'6', '0', '6', '1', '6', '2', '6', '3', '6', '4', '6', '5', '6', '6', '6',
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'7', '6', '8', '6', '9', '7', '0', '7', '1', '7', '2', '7', '3', '7', '4',
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'7', '5', '7', '6', '7', '7', '7', '8', '7', '9', '8', '0', '8', '1', '8',
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'2', '8', '3', '8', '4', '8', '5', '8', '6', '8', '7', '8', '8', '8', '9',
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'9', '0', '9', '1', '9', '2', '9', '3', '9', '4', '9', '5', '9', '6', '9',
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'7', '9', '8', '9', '9'};
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template <typename T>
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inline _LIBCPP_INLINE_VISIBILITY char*
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append1(char* buffer, T i)
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{
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*buffer = '0' + static_cast<char>(i);
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return buffer + 1;
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}
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template <typename T>
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inline _LIBCPP_INLINE_VISIBILITY char*
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append2(char* buffer, T i)
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{
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memcpy(buffer, &cDigitsLut[(i)*2], 2);
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return buffer + 2;
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}
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template <typename T>
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inline _LIBCPP_INLINE_VISIBILITY char*
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append3(char* buffer, T i)
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{
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return append2(append1(buffer, (i) / 100), (i) % 100);
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}
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template <typename T>
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inline _LIBCPP_INLINE_VISIBILITY char*
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append4(char* buffer, T i)
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{
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return append2(append2(buffer, (i) / 100), (i) % 100);
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}
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char*
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__u32toa(uint32_t value, char* buffer)
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{
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if (value < 10000)
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{
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if (value < 100)
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{
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if (value < 10)
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buffer = append1(buffer, value);
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else
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buffer = append2(buffer, value);
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}
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else
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{
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if (value < 1000)
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buffer = append3(buffer, value);
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else
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buffer = append4(buffer, value);
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}
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}
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else if (value < 100000000)
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{
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// value = bbbbcccc
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const uint32_t b = value / 10000;
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const uint32_t c = value % 10000;
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if (value < 1000000)
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{
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if (value < 100000)
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buffer = append1(buffer, b);
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else
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buffer = append2(buffer, b);
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}
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else
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{
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if (value < 10000000)
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buffer = append3(buffer, b);
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else
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buffer = append4(buffer, b);
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}
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buffer = append4(buffer, c);
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}
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else
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{
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// value = aabbbbcccc in decimal
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const uint32_t a = value / 100000000; // 1 to 42
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value %= 100000000;
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if (a < 10)
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buffer = append1(buffer, a);
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else
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buffer = append2(buffer, a);
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buffer = append4(buffer, value / 10000);
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buffer = append4(buffer, value % 10000);
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}
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return buffer;
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}
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char*
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__u64toa(uint64_t value, char* buffer)
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{
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if (value < 100000000)
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{
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uint32_t v = static_cast<uint32_t>(value);
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if (v < 10000)
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{
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if (v < 100)
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{
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if (v < 10)
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buffer = append1(buffer, v);
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else
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buffer = append2(buffer, v);
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}
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else
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{
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if (v < 1000)
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buffer = append3(buffer, v);
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else
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buffer = append4(buffer, v);
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}
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}
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else
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{
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// value = bbbbcccc
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const uint32_t b = v / 10000;
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const uint32_t c = v % 10000;
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if (v < 1000000)
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{
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if (v < 100000)
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buffer = append1(buffer, b);
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else
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buffer = append2(buffer, b);
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}
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else
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{
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if (v < 10000000)
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buffer = append3(buffer, b);
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else
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buffer = append4(buffer, b);
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}
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buffer = append4(buffer, c);
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}
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}
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else if (value < 10000000000000000)
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{
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const uint32_t v0 = static_cast<uint32_t>(value / 100000000);
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const uint32_t v1 = static_cast<uint32_t>(value % 100000000);
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const uint32_t b0 = v0 / 10000;
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const uint32_t c0 = v0 % 10000;
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if (v0 < 1000000)
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{
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if (v0 < 100000)
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buffer = append1(buffer, b0);
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else
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buffer = append2(buffer, b0);
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}
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else
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{
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if (v0 < 10000000)
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buffer = append3(buffer, b0);
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else
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buffer = append4(buffer, b0);
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}
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buffer = append4(buffer, c0);
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buffer = append4(buffer, v1 / 10000);
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buffer = append4(buffer, v1 % 10000);
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}
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else
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{
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const uint32_t a =
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static_cast<uint32_t>(value / 10000000000000000); // 1 to 1844
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value %= 10000000000000000;
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if (a < 100)
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{
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if (a < 10)
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buffer = append1(buffer, a);
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else
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buffer = append2(buffer, a);
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}
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else
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{
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if (a < 1000)
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buffer = append3(buffer, a);
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else
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buffer = append4(buffer, a);
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}
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const uint32_t v0 = static_cast<uint32_t>(value / 100000000);
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const uint32_t v1 = static_cast<uint32_t>(value % 100000000);
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buffer = append4(buffer, v0 / 10000);
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buffer = append4(buffer, v0 % 10000);
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buffer = append4(buffer, v1 / 10000);
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buffer = append4(buffer, v1 % 10000);
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}
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return buffer;
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}
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} // namespace __itoa
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_LIBCPP_END_NAMESPACE_STD
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