diff options
Diffstat (limited to 'parameter/FixedPointParameterType.cpp')
| -rw-r--r-- | parameter/FixedPointParameterType.cpp | 27 |
1 files changed, 24 insertions, 3 deletions
diff --git a/parameter/FixedPointParameterType.cpp b/parameter/FixedPointParameterType.cpp index 6a873b3..0f9369d 100644 --- a/parameter/FixedPointParameterType.cpp +++ b/parameter/FixedPointParameterType.cpp @@ -197,9 +197,27 @@ bool CFixedPointParameterType::fromBlackboard(string& strValue, const uint32_t& double dData = asDouble(iData); // Set up the precision of the display and notation type + // For a Qn.m number, the step between each storable number is 2^(-m). + // Hence, on a decimal representation, the Dth digit after the decimal + // point can take all possible values (1..9) - meaning that it is + // significant - only if + // + // 2^(-m) <= 10^(-D) + // -m <= log2(10^(-D)) + // -m <= log10(10^(-D)) / log10(2) + // -m <= -D / log10(2) + // m * log10(2) >= D + // + // Conversly, the Dth digit can be represented if + // + // D <= m * log10(2) + // + // Since floor(x) <= x, we can write (replacing D with iPrecision and m + // with _uiFractional) this next line. + // (we add 1 to avoid losing precision even though this last digit is + // not 100% significant) int iPrecision = (_uiFractional * log10(2.0)) + 1; - int iFactor = pow(10.0, iPrecision); - strStream << fixed << ((int64_t)(dData * iFactor)) / (double)iFactor; + strStream << fixed << setprecision(iPrecision) << dData; } strValue = strStream.str(); @@ -316,8 +334,11 @@ bool CFixedPointParameterType::checkValueAgainstRange(double dValue) const int32_t CFixedPointParameterType::asInteger(double dValue) const { // Do the conversion - int32_t iData = (int32_t)(dValue * (1UL << _uiFractional) + 0.5F - (double)(dValue < 0)); + // For Qn.m number, multiply by 2^n and round to the nearest integer + int32_t iData = (int32_t)(round(dValue * (1UL << _uiFractional))); // Left justify + // For a Qn.m number, shift 32 - (n + m + 1) bits to the left (the rest of + // the bits aren't used) iData <<= getSize() * 8 - getUtilSizeInBits(); return iData; |