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Fix BCH error correction

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This commit is contained in:
Jon Beniston
2026-07-31 16:49:10 +01:00
parent 874c0b9ffb
commit fe5d1ba155
1 changed files with 10 additions and 6 deletions
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plugins/channelrx/demodpager/pagerdemodsink.cpp
+10 -6
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@@ -247,7 +247,9 @@ bool PagerDemodSink::bchDecode(const quint32 cw, quint32& correctedCW)
return false;
}
correctedCW = result;
// The BCH decoder operates on bits 31 through 1. Preserve the separate
// overall parity bit in bit 0 so it can be checked after correction.
correctedCW = result | (cw & 0x1);
return true;
}
@@ -433,7 +435,7 @@ void PagerDemodSink::processOneSample(Complex &ci)
if ((m_bitCount == 32) && !m_gotSOP)
{
// Look for synccode that starts a batch - allow three errors that can be corrected
// Look for synccode that starts a batch - allow two errors that can be corrected
if (m_bits == PAGERDEMOD_POCSAG_SYNCCODE)
{
m_gotSOP = true;
@@ -444,19 +446,21 @@ void PagerDemodSink::processOneSample(Complex &ci)
m_gotSOP = true;
m_inverted = true;
}
else if (popcount(m_bits ^ PAGERDEMOD_POCSAG_SYNCCODE) >= 29)
else if (popcount(m_bits ^ PAGERDEMOD_POCSAG_SYNCCODE) <= 2)
{
quint32 correctedCW;
if (bchDecode(m_bits, correctedCW) && (correctedCW == PAGERDEMOD_POCSAG_SYNCCODE))
if (bchDecode(m_bits, correctedCW)
&& ((correctedCW & 0xfffffffeU) == (PAGERDEMOD_POCSAG_SYNCCODE & 0xfffffffeU)))
{
m_gotSOP = true;
m_inverted = false;
}
}
else if (popcount(m_bits ^ PAGERDEMOD_POCSAG_SYNCCODE_INV) >= 29)
else if (popcount(m_bits ^ PAGERDEMOD_POCSAG_SYNCCODE_INV) <= 2)
{
quint32 correctedCW;
if (bchDecode(~m_bits, correctedCW) && (correctedCW == PAGERDEMOD_POCSAG_SYNCCODE))
if (bchDecode(~m_bits, correctedCW)
&& ((correctedCW & 0xfffffffeU) == (PAGERDEMOD_POCSAG_SYNCCODE & 0xfffffffeU)))
{
m_gotSOP = true;
m_inverted = true;