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36 lines
1.2 KiB
36 lines
1.2 KiB
#include "parse_int.hpp" |
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#include <algorithm> |
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#include "utils/stdcompat/string_view.hpp" |
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namespace devilution { |
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uint8_t ParseFixed6Fraction(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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