[libcxx-commits] [libc] [libcxx] [llvm] [libcxx][libc] Hand in Hand PoC with from_chars (PR #91651)
Louis Dionne via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Aug 15 11:55:30 PDT 2024
================
@@ -0,0 +1,337 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
+#define _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
+
+// This header is in the shared LLVM-libc header library.
+#include "shared/str_to_float.h"
+
+#include <__assert>
+#include <__config>
+#include <cctype>
+#include <charconv>
+#include <concepts>
+#include <limits>
+#include <type_traits>
+
+// Included for the _Floating_type_traits class
+#include "to_chars_floating_point.h"
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// Parses an infinity string.
+// Valid strings are case insentitive and contain INF or INFINITY.
+//
+// - __first is the first argument to std::from_chars. When the string is invalid
+// this value is returned as ptr in the result.
+// - __last is the last argument of std::from_chars.
+// - __value is the value argument of std::from_chars,
+// - __ptr is the current position is the input string. This is points beyond
+// the initial I character.
+// - __negative whether a valid string represents -inf or +inf.
+template <floating_point _Fp>
+from_chars_result __from_chars_floating_point_inf(
+ const char* const __first, const char* __last, _Fp& __value, const char* __ptr, bool __negative) {
+ if (__last - __ptr < 2) [[unlikely]]
+ return {__first, errc::invalid_argument};
+
+ if (std::tolower(__ptr[0]) != 'n' || std::tolower(__ptr[1]) != 'f') [[unlikely]]
+ return {__first, errc::invalid_argument};
+
+ __ptr += 2;
+
+ // At this point the result is valid and contains INF.
+ // When the remaining part contains INITY this will be consumed. Otherwise
+ // only INF is consumed. For example INFINITZ will consume INF and ignore
+ // INITZ.
+
+ if (__last - __ptr >= 5 //
+ && std::tolower(__ptr[0]) == 'i' //
+ && std::tolower(__ptr[1]) == 'n' //
+ && std::tolower(__ptr[2]) == 'i' //
+ && std::tolower(__ptr[3]) == 't' //
+ && std::tolower(__ptr[4]) == 'y')
+ __ptr += 5;
+
+ if constexpr (numeric_limits<_Fp>::has_infinity) {
+ if (__negative)
+ __value = -std::numeric_limits<_Fp>::infinity();
+ else
+ __value = std::numeric_limits<_Fp>::infinity();
+
+ return {__ptr, std::errc{}};
+ } else {
+ return {__ptr, errc::result_out_of_range};
+ }
+}
+
+// Parses a nan string.
+// Valid strings are case insentitive and contain INF or INFINITY.
+//
+// - __first is the first argument to std::from_chars. When the string is invalid
+// this value is returned as ptr in the result.
+// - __last is the last argument of std::from_chars.
+// - __value is the value argument of std::from_chars,
+// - __ptr is the current position is the input string. This is points beyond
+// the initial N character.
+// - __negative whether a valid string represents -nan or +nan.
+template <floating_point _Fp>
+from_chars_result __from_chars_floating_point_nan(
+ const char* const __first, const char* __last, _Fp& __value, const char* __ptr, bool __negative) {
+ if (__last - __ptr < 2) [[unlikely]]
+ return {__first, errc::invalid_argument};
+
+ if (std::tolower(__ptr[0]) != 'a' || std::tolower(__ptr[1]) != 'n') [[unlikely]]
+ return {__first, errc::invalid_argument};
+
+ __ptr += 2;
+
+ // At this point the result is valid and contains NAN. When the remaining
+ // part contains ( n-char-sequence_opt ) this will be consumed. Otherwise
+ // only NAN is consumed. For example NAN(abcd will consume NAN and ignore
+ // (abcd.
+ if (__last - __ptr >= 2 && __ptr[0] == '(') {
+ size_t __offset = 1;
+ do {
+ if (__ptr[__offset] == ')') {
+ __ptr += __offset + 1;
+ break;
+ }
+ if (__ptr[__offset] != '_' && !std::isalnum(__ptr[__offset]))
+ break;
+ ++__offset;
+ } while (__ptr + __offset != __last);
+ }
+
+ if (__negative)
+ __value = -std::numeric_limits<_Fp>::quiet_NaN();
+ else
+ __value = std::numeric_limits<_Fp>::quiet_NaN();
+
+ return {__ptr, std::errc{}};
+}
+
+template <floating_point _Fp>
+from_chars_result __from_chars_floating_point_decimal(
+ const char* const __first,
+ const char* __last,
+ _Fp& __value,
+ chars_format __fmt,
+ const char* __ptr,
+ bool __negative) {
+ using _Traits = _Floating_type_traits<_Fp>;
+ using _Uint_type = typename _Traits::_Uint_type;
+
+ const char* src = __ptr; // rename to match the libc code copied for this section.
+ ptrdiff_t length = __last - src;
+ _LIBCPP_ASSERT_INTERNAL(length > 0, "");
+
+ _Uint_type mantissa = 0;
+ int exponent = 0;
+ bool truncated = false;
+ bool seen_digit = false;
+ bool has_valid_exponent = false;
+ bool after_decimal = false;
+ size_t index = 0;
+ const size_t BASE = 10;
+ constexpr char EXPONENT_MARKER = 'e';
+ constexpr char DECIMAL_POINT = '.';
+
+ // The loop fills the mantissa with as many digits as it can hold
+ const _Uint_type bitstype_max_div_by_base = numeric_limits<_Uint_type>::max() / BASE;
+
+ while (index < static_cast<size_t>(length)) {
+ if (LIBC_NAMESPACE::internal::isdigit(src[index])) {
+ uint32_t digit = src[index] - '0';
+ seen_digit = true;
+
+ if (mantissa < bitstype_max_div_by_base) {
+ mantissa = (mantissa * BASE) + digit;
+ if (after_decimal) {
+ --exponent;
+ }
+ } else {
+ if (digit > 0)
+ truncated = true;
+ if (!after_decimal)
+ ++exponent;
+ }
+
+ ++index;
+ continue;
+ }
+ if (src[index] == DECIMAL_POINT) {
+ if (after_decimal) {
+ break; // this means that src[index] points to a second decimal point, ending the number.
+ }
+ after_decimal = true;
+ ++index;
+ continue;
+ }
+ // The character is neither a digit nor a decimal point.
+ break;
+ }
+
+ if (!seen_digit)
+ return {__first, errc::invalid_argument};
+
+ if (index < static_cast<size_t>(length) && LIBC_NAMESPACE::internal::tolower(src[index]) == EXPONENT_MARKER) {
+ bool has_sign = false;
+ if (index + 1 < static_cast<size_t>(length) && (src[index + 1] == '+' || src[index + 1] == '-')) {
+ has_sign = true;
+ }
+ if (index + 1 + static_cast<size_t>(has_sign) < static_cast<size_t>(length) &&
+ LIBC_NAMESPACE::internal::isdigit(src[index + 1 + static_cast<size_t>(has_sign)])) {
+ has_valid_exponent = true;
+ ++index;
+ auto result =
+ LIBC_NAMESPACE::internal::strtointeger<int32_t>(src + index, 10, static_cast<size_t>(length) - index);
+ // if (result.has_error())
+ // output.error = result.error;
+ int32_t add_to_exponent = result.value;
+ index += result.parsed_len;
+
+ // Here we do this operation as int64 to avoid overflow.
+ int64_t temp_exponent = static_cast<int64_t>(exponent) + static_cast<int64_t>(add_to_exponent);
+
+ // If the result is in the valid range, then we use it. The valid range is
+ // also within the int32 range, so this prevents overflow issues.
+ if (temp_exponent > LIBC_NAMESPACE::fputil::FPBits<_Fp>::MAX_BIASED_EXPONENT) {
+ exponent = LIBC_NAMESPACE::fputil::FPBits<_Fp>::MAX_BIASED_EXPONENT;
+ } else if (temp_exponent < -LIBC_NAMESPACE::fputil::FPBits<_Fp>::MAX_BIASED_EXPONENT) {
+ exponent = -LIBC_NAMESPACE::fputil::FPBits<_Fp>::MAX_BIASED_EXPONENT;
+ } else {
+ exponent = static_cast<int32_t>(temp_exponent);
+ }
+ }
+ }
+
+ // [charconv.from.chars]
+ switch (__fmt) {
+ case chars_format::scientific:
+ // 6.2 if fmt has chars_format::scientific set but not chars_format::fixed,
+ // the otherwise optional exponent part shall appear;
+ if (!has_valid_exponent)
+ return {__first, errc::invalid_argument};
+ break;
+ case chars_format::fixed:
+ // 6.3 if fmt has chars_format::fixed set but not chars_format::scientific,
+ // the optional exponent part shall not appear;
+ if (has_valid_exponent)
+ return {__first, errc::invalid_argument};
+ break;
+ case chars_format::general:
+ case chars_format::hex: // impossible but it silences the compiler
+ break;
+ }
+
+ LIBC_NAMESPACE::internal::ExpandedFloat<_Fp> expanded_float = {0, 0};
+ errc status{};
+ if (mantissa != 0) {
+ auto temp = LIBC_NAMESPACE::shared::decimal_exp_to_float<_Fp>(
+ {mantissa, exponent}, truncated, LIBC_NAMESPACE::internal::RoundDirection::Nearest, src, length);
+ expanded_float = temp.num;
+ if (temp.error == ERANGE) {
+ status = errc::result_out_of_range;
+ }
+ }
+
+ auto result = LIBC_NAMESPACE::fputil::FPBits<_Fp>();
+ result.set_mantissa(expanded_float.mantissa);
+ result.set_biased_exponent(expanded_float.exponent);
+
+ // C17 7.12.1/6
+ // The result underflows if the magnitude of the mathematical result is so
+ // small that the mathematical re- sult cannot be represented, without
+ // extraordinary roundoff error, in an object of the specified type.237) If
+ // the result underflows, the function returns an implementation-defined
+ // value whose magnitude is no greater than the smallest normalized positive
+ // number in the specified type; if the integer expression math_errhandling
+ // & MATH_ERRNO is nonzero, whether errno acquires the value ERANGE is
+ // implementation-defined; if the integer expression math_errhandling &
+ // MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point
+ // exception is raised is implementation-defined.
+ //
+ // LLLVM-LIBC sets ERAGNE for subnormal values
+ //
+ // [charconv.from.chars]/1
+ // ... If the parsed value is not in the range representable by the type of
+ // value, value is unmodified and the member ec of the return value is
+ // equal to errc::result_out_of_range. ...
+ //
+ // Undo the ERANGE for subnormal values.
+ if (status == errc::result_out_of_range && result.is_subnormal() && !result.is_zero())
+ status = errc{};
+
+ if (__negative)
+ __value = -result.get_val();
+ else
+ __value = result.get_val();
+
+ return {src + index, status};
+}
+
+template <floating_point _Fp>
+from_chars_result
+__from_chars_floating_point(const char* const __first, const char* __last, _Fp& __value, chars_format __fmt) {
+ if (__first == __last) [[unlikely]]
+ return {__first, errc::invalid_argument};
+
+ const char* __ptr = __first;
+ bool __negative = *__ptr == '-';
+ if (__negative) {
+ ++__ptr;
+ if (__ptr == __last) [[unlikely]]
+ return {__first, errc::invalid_argument};
+ }
+
+ // [charconv.from.chars]
+ // [Note 1: If the pattern allows for an optional sign, but the string has
+ // no digit characters following the sign, no characters match the pattern.
+ // — end note]
+ // This is true for integrals, floating point allows -.0
+ switch (std::tolower(*__ptr)) {
+ case 'i':
+ // TODO Evaluate the other implementations
+ // [charconv.from.chars]/6.2
+ // if fmt has chars_format::scientific set but not chars_format::fixed,
+ // the otherwise optional exponent part shall appear;
+ // Since INF/NAN do not have an exponent this value is not valid.
+ // See LWG3456
+ if (__fmt == chars_format::scientific)
+ return {__first, errc::invalid_argument};
+
+ return __from_chars_floating_point_inf(__first, __last, __value, __ptr + 1, __negative);
----------------
ldionne wrote:
Also below. Although not needed strictly speaking, we consistently qualify free function calls to avoid unintended ADL.
```suggestion
return std::__from_chars_floating_point_inf(__first, __last, __value, __ptr + 1, __negative);
```
https://github.com/llvm/llvm-project/pull/91651
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