From fb00002f0136b8c19a5c86499164bbc57da4edb7 Mon Sep 17 00:00:00 2001 From: Benjamin Barenblat Date: Mon, 11 Oct 2021 17:07:08 -0400 Subject: dewpoint, a tool to calculate dew points --- .gitignore | 16 +++++ LICENSE | 202 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ build.ninja | 26 ++++++++ dewpoint.cc | 163 ++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 407 insertions(+) create mode 100644 .gitignore create mode 100644 LICENSE create mode 100644 build.ninja create mode 100644 dewpoint.cc diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..0082cc7 --- /dev/null +++ b/.gitignore @@ -0,0 +1,16 @@ +# Copyright 2021 Benjamin Barenblat +# +# Licensed under the Apache License, Version 2.0 (the "License"); you may not +# use this file except in compliance with the License. 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You may obtain a copy of +# the License at +# +# https://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, software +# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT +# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the +# License for the specific language governing permissions and limitations under +# the License. + +cxx = g++ + +cxxflags = -std=c++17 -Wall -Wextra -Wno-sign-compare -fdiagnostics-show-template-tree -pipe -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -O3 -DNDEBUG -fstack-protector-strong -ffunction-sections -fdata-sections -flto + +ldflags = -flto -Wl,-O2 -Wl,-z,relro -Wl,--gc-sections -Wl,--as-needed + +rule cxxld + command = $cxx $cxxflags $ldflags $in -o $out $libs + description = Compiling and linking $out + +build dewpoint: cxxld dewpoint.cc + libs = -lm diff --git a/dewpoint.cc b/dewpoint.cc new file mode 100644 index 0000000..4acb9e9 --- /dev/null +++ b/dewpoint.cc @@ -0,0 +1,163 @@ +// Copyright 2021 Benjamin Barenblat +// +// Licensed under the Apache License, Version 2.0 (the "License"); you may not +// use this file except in compliance with the License. You may obtain a copy of +// the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT +// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the +// License for the specific language governing permissions and limitations under +// the License. + +#include +#include +#include +#include + +#include +#include +#include + +namespace { + +constexpr std::string_view kShortUsage = + "Usage: dewpoint TEMPERATURE HUMIDITY\n"; + +constexpr std::string_view kHelp = + R"(Compute the dew point from a given temperature and humidity. Temperatures are +interpreted by default according to the current locale; humidity is interpreted +as a percentage. + +Options: + -c, --celsius, --centigrade + use the Celsius temperature scale + -f, --fahrenheit use the Fahrenheit temperature scale + --help display this help and exit +)"; + +constexpr std::string_view kAskForHelp = + "Try 'dewpoint --help' for more information\n"; + +enum { + kHelpLongOption = 128, +}; + +bool LocaleUsesFahrenheit(std::string_view locale) { + int underscore = locale.find('_'); + int dot = locale.find('.'); + if (underscore == std::string_view::npos || dot == std::string_view::npos || + dot <= underscore) { + return false; + } + std::string_view territory = + locale.substr(underscore + 1, dot - underscore - 1); + return territory == "US" /* United States */ || + territory == "LR" /* Liberia */ || + territory == "FM" /* Micronesia */ || + territory == "KY" /* Cayman Islands */ || + territory == "MH" /* Marshall Islands */ || + territory == "PW" /* Palau */; +} + +std::optional ReadFloat(const char* s) { + char* end; + float f = strtof(s, &end); + if (*end != '\0') { + return std::nullopt; + } + return f; +} + +// Approximates the dew point of air at the specified temperature and relative +// humidity using the Magnus formula. For a complete derivation, see equation 8 +// of Mark G. Lawrence, "The Relationship Between Relative Humidity and the +// Dewpoint Temperature in Moist Air," Bulletin of the American Meteorological +// Society 86(2) (February 2005), 225-234, +// https://doi.org/10.1175/BAMS-86-2-225. +float DewPoint(float celsius, float humidity) { + constexpr float kA = 17.625; + constexpr float kB = 243.04; + + float x = log(humidity * 0.01f) + kA * celsius / (kB + celsius); + return kB * x / (kA - x); +} + +float DewPointFahrenheit(float fahrenheit, float humidity) { + return 9.0f / 5.0f * DewPoint(5.0f / 9.0f * (fahrenheit - 32.0f), humidity) + + 32.0f; +} + +} // namespace + +int main(int argc, char* argv[]) { + setlocale(LC_ALL, ""); + + std::string measurement_locale = "C"; + if (const char* s = setlocale(LC_MEASUREMENT, ""); s != nullptr) { + measurement_locale = s; + } + + const bool locale_uses_fahrenheit = LocaleUsesFahrenheit(measurement_locale); + bool use_fahrenheit = locale_uses_fahrenheit; + + static option long_options[] = { + {"celsius", no_argument, nullptr, 'c'}, + {"centigrade", no_argument, nullptr, 'c'}, + {"fahrenheit", no_argument, nullptr, 'f'}, + {"help", no_argument, nullptr, kHelpLongOption}, + {nullptr, 0, nullptr, 0}, + }; + while (true) { + int c = getopt_long(argc, argv, "cf", long_options, nullptr); + if (c == -1) { + break; + } + switch (c) { + case 'c': + use_fahrenheit = false; + break; + case 'f': + use_fahrenheit = true; + break; + case kHelpLongOption: + std::cout << kShortUsage << kHelp + << "\nYour current measurement locale is " + << measurement_locale << ", which uses " + << (locale_uses_fahrenheit ? "Fahrenheit" : "Celsius") + << " by\ndefault.\n"; + return 0; + case '?': + std::cerr << kAskForHelp; + return 1; + default: + std::cerr << "Internal error; please report.\n"; + return 1; + } + } + + if (optind != argc - 2) { + std::cerr << kShortUsage << kAskForHelp; + return 1; + } + + std::optional temperature = ReadFloat(argv[1]); + if (!temperature.has_value()) { + std::cerr << "dewpoint: invalid temperature \"" << argv[1] << "\"\n" + << kAskForHelp; + return 1; + } + + std::optional humidity = ReadFloat(argv[2]); + if (!humidity.has_value() || *humidity <= 0.0f) { + std::cerr << "dewpoint: invalid humidity \"" << argv[1] << "\"\n" + << kAskForHelp; + return 1; + } + + float dew_point = use_fahrenheit ? DewPointFahrenheit(*temperature, *humidity) + : DewPoint(*temperature, *humidity); + std::cout << static_cast(rintf(dew_point)) << '\n'; +} -- cgit v1.2.3