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35 lines
1.1 KiB
35 lines
1.1 KiB
3 years ago
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#include "parse_int.hpp"
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#include <algorithm>
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namespace devilution {
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uint8_t ParseFixed6Fraction(std::string_view str, const char **endOfParse)
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{
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unsigned numDigits = 0;
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uint32_t decimalFraction = 0;
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// Read at most 7 digits, at that threshold we're able to determine an exact rounding for 6 bit fixed point numbers
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while (!str.empty() && numDigits < 7) {
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if (str[0] < '0' || str[0] > '9') {
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break;
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}
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decimalFraction = decimalFraction * 10 + str[0] - '0';
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++numDigits;
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str.remove_prefix(1);
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}
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if (endOfParse != nullptr) {
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// to mimic the behaviour of std::from_chars consume all remaining digits in case the value was overly precise.
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*endOfParse = std::find_if_not(str.data(), str.data() + str.size(), [](char character) { return character >= '0' && character <= '9'; });
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}
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// to ensure rounding to nearest we normalise all values to 7 decimal places
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while (numDigits < 7) {
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decimalFraction *= 10;
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++numDigits;
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}
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// we add half the step between representable values to use integer truncation as a substitute for rounding to nearest.
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return (decimalFraction + 78125) / 156250;
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}
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} // namespace devilution
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