meCoffee_in_CPP/lib/meCoffee_controller_logic/src/numeric_conversion.cpp

#include "numeric_conversion.h"

#include <string.h>

#include "hardware_seam.h"
#include "program_memory.h"

namespace meCoffee {

namespace {

// binary32 bit patterns for 10^-w and 10^+w with w = 1, 2, 4, 8, 16, 32.
const uint32_t kNegativeDecimalPowerBitPatterns[6] MECOFFEE_PROGRAM_MEMORY = {
    0x3dcccccdUL, 0x3c23d70aUL, 0x38d1b717UL, 0x322bcc77UL, 0x24e69595UL, 0x0a4fb11fUL};
const uint32_t kPositiveDecimalPowerBitPatterns[6] MECOFFEE_PROGRAM_MEMORY = {
    0x41200000UL, 0x42c80000UL, 0x461c4000UL, 0x4cbebc20UL, 0x5a0e1bcaUL, 0x749dc5aeUL};
const uint8_t kDecimalPowerWeights[6] = {1, 2, 4, 8, 16, 32};

constexpr uint32_t kSignificandOverflowThreshold = 429496728UL;
constexpr uint16_t kExponentDigitFreezeThreshold = 3200;
constexpr uint32_t kCanonicalNotANumberBitPattern = 0x7fc00000UL;
constexpr uint32_t kPositiveInfinityBitPattern = 0x7f800000UL;

float reinterpretBitPatternAsFloat(uint32_t bitPattern) {
    float reinterpretedValue;
    memcpy(&reinterpretedValue, &bitPattern, sizeof reinterpretedValue);
    return reinterpretedValue;
}

uint32_t reinterpretFloatAsBitPattern(float numericValue) {
    uint32_t bitPattern;
    memcpy(&bitPattern, &numericValue, sizeof bitPattern);
    return bitPattern;
}

uint32_t readProgramMemoryUnsigned32(const uint32_t* programMemoryAddress) {
    const uint8_t* firstByte = reinterpret_cast<const uint8_t*>(programMemoryAddress);
    uint32_t assembledValue = 0;
    for (uint8_t byteIndex = 0; byteIndex < 4; ++byteIndex) {
        assembledValue |= static_cast<uint32_t>(hardware::readProgramMemoryByte(firstByte + byteIndex))
                          << (8 * byteIndex);
    }
    return assembledValue;
}

bool isWhitespaceCharacter(char character) {
    return character == ' ' || (character >= 0x09 && character <= 0x0d);
}

bool isDecimalDigit(char character) { return character >= '0' && character <= '9'; }

char toLowerCaseLetter(char character) {
    return (character >= 'A' && character <= 'Z') ? static_cast<char>(character + ('a' - 'A')) : character;
}

bool startsWithCaseInsensitive(const char* text, const char* lowerCasePrefix) {
    while (*lowerCasePrefix != '\0') {
        if (toLowerCaseLetter(*text) != *lowerCasePrefix) {
            return false;
        }
        ++text;
        ++lowerCasePrefix;
    }
    return true;
}

}  // namespace

float parseDecimalFloatingPoint(const char* text, DecimalParseDiagnostics* diagnostics) {
    DecimalParseDiagnostics localDiagnostics = {};
    DecimalParseDiagnostics& recorded = diagnostics != nullptr ? *diagnostics : localDiagnostics;
    recorded = DecimalParseDiagnostics{};

    const char* cursor = text;
    while (isWhitespaceCharacter(*cursor)) {
        ++cursor;
    }
    bool isNegative = false;
    if (*cursor == '-') {
        isNegative = true;
        ++cursor;
    } else if (*cursor == '+') {
        ++cursor;
    }

    if (startsWithCaseInsensitive(cursor, "nan")) {
        recorded.consumedCharacterCount = static_cast<uint16_t>(cursor + 3 - text);
        return reinterpretBitPatternAsFloat(kCanonicalNotANumberBitPattern);
    }
    if (startsWithCaseInsensitive(cursor, "inf")) {
        cursor += 3;
        if (startsWithCaseInsensitive(cursor, "inity")) {
            cursor += 5;
        }
        recorded.consumedCharacterCount = static_cast<uint16_t>(cursor - text);
        return reinterpretBitPatternAsFloat(kPositiveInfinityBitPattern | (isNegative ? 0x80000000UL : 0));
    }

    uint32_t significand = 0;
    uint16_t decimalExponentOffset = 0;
    uint16_t discardedDigitCount = 0;
    bool hasSignificandDigit = false;
    bool hasSeenDecimalPoint = false;
    bool isDiscardingDigits = false;

    for (;; ++cursor) {
        const char character = *cursor;
        if (isDecimalDigit(character)) {
            hasSignificandDigit = true;
            if (isDiscardingDigits) {
                ++discardedDigitCount;
                if (!hasSeenDecimalPoint) {
                    ++decimalExponentOffset;
                }
            } else {
                if (hasSeenDecimalPoint) {
                    --decimalExponentOffset;
                }
                significand = significand * 10 + static_cast<uint8_t>(character - '0');
                if (significand >= kSignificandOverflowThreshold) {
                    isDiscardingDigits = true;
                }
            }
        } else if (character == '.' && !hasSeenDecimalPoint) {
            hasSeenDecimalPoint = true;
        } else {
            break;
        }
    }

    if (!hasSignificandDigit) {
        return 0.0f;
    }

    if (*cursor == 'e' || *cursor == 'E') {
        const char* exponentCursor = cursor + 1;
        bool isExponentNegative = false;
        if (*exponentCursor == '-') {
            isExponentNegative = true;
            ++exponentCursor;
        } else if (*exponentCursor == '+') {
            ++exponentCursor;
        }
        if (isDecimalDigit(*exponentCursor)) {
            uint16_t explicitExponent = 0;
            while (isDecimalDigit(*exponentCursor)) {
                if (explicitExponent < kExponentDigitFreezeThreshold) {
                    explicitExponent = static_cast<uint16_t>(explicitExponent * 10 + (*exponentCursor - '0'));
                }
                ++exponentCursor;
            }
            decimalExponentOffset = static_cast<uint16_t>(
                decimalExponentOffset + (isExponentNegative ? static_cast<uint16_t>(0 - explicitExponent) : explicitExponent));
            cursor = exponentCursor;
        }
    }

    recorded.retainedSignificand = significand;
    recorded.decimalExponentOffset = static_cast<int16_t>(decimalExponentOffset);
    recorded.discardedSignificandDigitCount = discardedDigitCount;
    recorded.consumedCharacterCount = static_cast<uint16_t>(cursor - text);

    float scaledValue = static_cast<float>(significand);
    if (isNegative) {
        scaledValue = -scaledValue;
    }
    if (significand == 0) {
        return scaledValue;
    }

    const int16_t signedExponentOffset = static_cast<int16_t>(decimalExponentOffset);
    const bool isScalingDownward = signedExponentOffset < 0;
    uint16_t remainingExponentMagnitude = isScalingDownward
        ? static_cast<uint16_t>(0 - static_cast<uint16_t>(signedExponentOffset))
        : static_cast<uint16_t>(signedExponentOffset);
    const uint32_t* powerTable = isScalingDownward ? kNegativeDecimalPowerBitPatterns : kPositiveDecimalPowerBitPatterns;

    for (int8_t weightIndex = 5; weightIndex >= 0; --weightIndex) {
        const float decimalPower = reinterpretBitPatternAsFloat(readProgramMemoryUnsigned32(&powerTable[weightIndex]));
        while (remainingExponentMagnitude >= kDecimalPowerWeights[weightIndex]) {
            scaledValue *= decimalPower;
            remainingExponentMagnitude = static_cast<uint16_t>(remainingExponentMagnitude - kDecimalPowerWeights[weightIndex]);
        }
    }

    const uint32_t scaledBitPattern = reinterpretFloatAsBitPattern(scaledValue);
    const bool isInfinite = (scaledBitPattern & 0x7fffffffUL) == kPositiveInfinityBitPattern;
    const bool isZero = (scaledBitPattern & 0x7fffffffUL) == 0;
    recorded.isOutOfRangeIndicatorRaised = isInfinite || isZero;
    return scaledValue;
}

uint32_t convertFloatToUnsigned32(float numericValue, bool* isConversionStatusFlagged) {
    bool isFlagged = false;
    uint32_t convertedValue = 0;

    const uint32_t bitPattern = reinterpretFloatAsBitPattern(numericValue);
    const bool isNegative = (bitPattern & 0x80000000UL) != 0;
    const uint8_t biasedExponent = static_cast<uint8_t>((bitPattern >> 23) & 0xff);

    if (biasedExponent == 0xff) {
        isFlagged = true;
    } else if (biasedExponent >= 127) {
        const uint8_t unbiasedExponent = static_cast<uint8_t>(biasedExponent - 127);
        if (unbiasedExponent >= 32) {
            isFlagged = true;
        } else {
            const uint32_t significandWithHiddenBit = (bitPattern & 0x007fffffUL) | 0x00800000UL;
            const uint32_t magnitude = unbiasedExponent >= 23
                ? significandWithHiddenBit << (unbiasedExponent - 23)
                : significandWithHiddenBit >> (23 - unbiasedExponent);
            if (magnitude >= 0x80000000UL) {
                isFlagged = true;
            }
            convertedValue = isNegative ? static_cast<uint32_t>(0 - magnitude) : magnitude;
        }
    }

    if (isConversionStatusFlagged != nullptr) {
        *isConversionStatusFlagged = isFlagged;
    }
    return convertedValue;
}

int32_t convertFloatToSigned32(float numericValue) {
    bool isFlagged = false;
    const uint32_t convertedValue = convertFloatToUnsigned32(numericValue, &isFlagged);
    if (isFlagged) {
        return INT32_MIN;
    }
    return static_cast<int32_t>(convertedValue);
}

namespace {

uint32_t parseIntegerPrefix(const char* text, uint8_t bitWidth) {
    const char* cursor = text;
    while (isWhitespaceCharacter(*cursor)) {
        ++cursor;
    }
    bool isNegative = false;
    if (*cursor == '-') {
        isNegative = true;
        ++cursor;
    } else if (*cursor == '+') {
        ++cursor;
    }
    uint32_t accumulated = 0;
    while (isDecimalDigit(*cursor)) {
        accumulated = accumulated * 10 + static_cast<uint8_t>(*cursor - '0');
        ++cursor;
    }
    if (isNegative) {
        accumulated = 0 - accumulated;
    }
    return bitWidth == 16 ? (accumulated & 0xffffUL) : accumulated;
}

}  // namespace

uint16_t parseIntegerPrefixModulo65536(const char* text) {
    return static_cast<uint16_t>(parseIntegerPrefix(text, 16));
}

uint32_t parseIntegerPrefixModulo4294967296(const char* text) { return parseIntegerPrefix(text, 32); }

uint8_t formatUnsignedDecimal(uint32_t numericValue, char* outputBuffer) {
    char reversedDigits[10];
    uint8_t digitCount = 0;
    do {
        reversedDigits[digitCount++] = static_cast<char>('0' + numericValue % 10);
        numericValue /= 10;
    } while (numericValue != 0);
    for (uint8_t position = 0; position < digitCount; ++position) {
        outputBuffer[position] = reversedDigits[digitCount - 1 - position];
    }
    return digitCount;
}

uint8_t formatSignedDecimal(int32_t numericValue, char* outputBuffer) {
    if (numericValue < 0) {
        outputBuffer[0] = '-';
        return static_cast<uint8_t>(1 + formatUnsignedDecimal(0 - static_cast<uint32_t>(numericValue), outputBuffer + 1));
    }
    return formatUnsignedDecimal(static_cast<uint32_t>(numericValue), outputBuffer);
}

}  // namespace meCoffee