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formats/tzx_cas.cpp: Fixed regression in TAP format; Added checksum validation (MT9104) #13322

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merged 1 commit into from
Feb 2, 2025
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formats/tzx_cas.cpp: Fixed regression in TAP format; Added checksum validation (MT9104) #13322

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50 changes: 38 additions & 12 deletions src/lib/formats/tzx_cas.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -804,31 +804,56 @@ static int cdt_cas_fill_wave( int16_t *buffer, int length, const uint8_t *bytes
return size;
}

static int tap_cas_to_wav_size( const uint8_t *casdata, int caslen )
static int tap_cas_to_wav_size(const uint8_t *casdata, int caslen)
{
/*
TAP Header:
| 0 | W | Length of Data Block (N) | -+
| 2 | B | Flag Byte | -+
| 3 | B*(N-2) | Data | | Data Block
| N+1 | B | XOR Checksum of [2..N] | -+
*/

int size = 0;
const uint8_t *p = casdata;

while (caslen > 0)
while (caslen > 2)
{
int data_size = get_u16le(&p[0]);
int pilot_length = (p[2] == 0x00) ? 8063 : 3223;
caslen -= data_size;
if (caslen < 0)
p += 2;
caslen -= 2;
if (caslen < data_size)
{
LOG_FORMATS("tap_cas_to_wav_size: Requested 0x%X byte but only 0x%X available.\n", data_size, data_size + caslen);
data_size += caslen;
LOG_FORMATS("tap_cas_to_wav_size: Requested 0x%X bytes but only 0x%X available.\n", data_size, caslen);
data_size = caslen;
}
caslen -= data_size;

// Data Block
LOG_FORMATS("tap_cas_to_wav_size: Handling TAP block containing 0x%X bytes", data_size);
p += 2;
const int pilot_length = (p[0] == 0x00) ? 8063 : 3223;
size += tzx_cas_handle_block(nullptr, p, 1000, data_size, 2168, pilot_length, 667, 735, 855, 1710, 8);
LOG_FORMATS(", total size is now: %d\n", size);
LOG_FORMATS(", total size is now: %d", size);

// Validate Checksum
const uint8_t checksum = p[data_size - 1];
LOG_FORMATS(", checksum 0x%X\n", checksum);
uint8_t check = 0x00;
for(int i = 0; i < (data_size - 1); i++)
{
check ^= p[i];
}
if (check != checksum)
{
LOG_FORMATS("tap_cas_to_wav_size: wrong checksum 0x%X\n", check);
}

p += data_size;
}
return size;
}

static int tap_cas_fill_wave( int16_t *buffer, int length, const uint8_t *bytes )
static int tap_cas_fill_wave(int16_t *buffer, int length, const uint8_t *bytes)
{
int16_t *p = buffer;
int size = 0;
Expand All @@ -837,7 +862,9 @@ static int tap_cas_fill_wave( int16_t *buffer, int length, const uint8_t *bytes
while (size < length)
{
int data_size = get_u16le(&bytes[0]);
int pilot_length = (bytes[2] == 0x00) ? 8063 : 3223;
bytes += 2;

int pilot_length = (bytes[0] == 0x00) ? 8063 : 3223;
LOG_FORMATS("tap_cas_fill_wave: Handling TAP block containing 0x%X bytes\n", data_size);
/*
length -= data_size;
Expand All @@ -846,7 +873,6 @@ static int tap_cas_fill_wave( int16_t *buffer, int length, const uint8_t *bytes
data_size += length; // Take as much as we can.
}
*/
bytes += 2;
size += tzx_cas_handle_block(&p, bytes, 1000, data_size, 2168, pilot_length, 667, 735, 855, 1710, 8);
bytes += data_size;
}
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