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Pack and unpack using shifting and masking

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This commit is contained in:
Geoffrey Merck 2020-05-08 16:41:06 +02:00
parent 5e887a95c5
commit 8cdc1ffe7f
2 changed files with 35 additions and 22 deletions
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46
FMControl.cpp
View file

@ -49,21 +49,17 @@ bool CFMControl::writeModem(const unsigned char* data, unsigned int length)
for (unsigned int i = 0U; i < length; i += 3U) { for (unsigned int i = 0U; i < length; i += 3U) {
unsigned short sample1 = 0U; unsigned short sample1 = 0U;
unsigned short sample2 = 0U; unsigned short sample2 = 0U;
unsigned short MASK = 0x0001U; unsigned short MASK = ~(0xFFFFF000);
const unsigned char* base = data + i; int pack = 0;
for (unsigned int j = 0U; j < 12U; j++, MASK <<= 1) { char* packPointer = (char*)&pack;
unsigned int pos1 = j;
unsigned int pos2 = j + 12U;
bool b1 = READ_BIT(base, pos1) != 0U; packPointer[1] = data[i];
bool b2 = READ_BIT(base, pos2) != 0U; packPointer[2] = data[i + 1];
packPointer[3] = data[i + 2];
if (b1) sample2 = (short)(pack & MASK);
sample1 |= MASK; sample1 = (short)(pack >> 12);
if (b2)
sample2 |= MASK;
}
// Convert from unsigned short (0 - +4095) to float (-1.0 - +1.0) // Convert from unsigned short (0 - +4095) to float (-1.0 - +1.0)
samples[nSamples++] = (float(sample1) - 2048.0F) / 2048.0F; samples[nSamples++] = (float(sample1) - 2048.0F) / 2048.0F;
@ -108,18 +104,24 @@ unsigned int CFMControl::readModem(unsigned char* data, unsigned int space)
// Pre-emphasise the data and other stuff. // Pre-emphasise the data and other stuff.
// Pack the floating point data (+1.0 to -1.0) to packed 12-bit samples (+2047 - -2048) // Pack the floating point data (+1.0 to -1.0) to packed 12-bit samples (+2047 - -2048)
unsigned int offset = 0U; int pack = 0;
for (unsigned int i = 0U; i < nSamples; i++) { char* packPointer = (char*)&pack;
unsigned short sample = (unsigned short)((samples[i] + 1.0F) * 2048.0F + 0.5F); unsigned int j = 0U;
unsigned short MASK = 0x0001U; unsigned int i = 0U;
for (unsigned int j = 0U; j < 12U; j++, MASK <<= 1) { for (; i < nSamples && j < space; i += 2, j += 3) {
bool b = (sample & MASK) != 0U; unsigned short sample1 = (unsigned short)((samples[i] + 1.0F) * 2048.0F + 0.5F);
WRITE_BIT(data, offset, b); unsigned short sample2 = (unsigned short)((samples[i + 1] + 1.0F) * 2048.0F + 0.5F);
offset++;
} pack = 0;
pack = ((int)sample1) << 12;
pack |= sample2;
data[j] = packPointer[1];
data[j + 1] = packPointer[2];
data[j + 2] = packPointer[3];
} }
return nSamples; return j;//return the number of bytes written
} }
void CFMControl::clock(unsigned int ms) void CFMControl::clock(unsigned int ms)

11
FMControl.h
View file

@ -22,6 +22,17 @@
#include "FMNetwork.h" #include "FMNetwork.h"
#include "Defines.h" #include "Defines.h"
typedef struct
{
union
{
int pack;
char packBytes[4];
};
} SamplePack;
class CFMControl { class CFMControl {
public: public:
CFMControl(CFMNetwork* network); CFMControl(CFMNetwork* network);