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#include "s2_scrambling.h"
/*
Adapted from LeanDVB
*/
namespace dvbs2
{
S2Scrambling::S2Scrambling(int codenum)
{
uint32_t stx = 0x00001, sty = 0x3ffff;
// x starts at codenum, wraps at index 2^18-1 by design
for (int i = 0; i < codenum; ++i)
stx = lfsr_x(stx);
// First half of sequence is LSB of scrambling angle
for (int i = 0; i < 131072; ++i)
{
int zn = (stx ^ sty) & 1;
Rn[i] = zn;
stx = lfsr_x(stx);
sty = lfsr_y(sty);
}
// Second half is MSB
for (int i = 0; i < 131072; ++i)
{
int zn = (stx ^ sty) & 1;
Rn[i] |= zn << 1;
stx = lfsr_x(stx);
sty = lfsr_y(sty);
}
}
S2Scrambling::~S2Scrambling()
{
}
void S2Scrambling::reset()
{
pos = 0;
}
complex_t S2Scrambling::descramble(complex_t &p)
{
r = Rn[pos++];
switch (r)
{
case 3:
res.real = -p.imag;
res.imag = p.real;
break;
case 2:
res.real = -p.real;
res.imag = -p.imag;
break;
case 1:
res.real = p.imag;
res.imag = -p.real;
break;
default:
res = p;
}
return res;
}
complex_t S2Scrambling::scramble(complex_t &p)
{
r = Rn[pos++];
switch (r)
{
case 3:
res.imag = -p.real;
res.real = p.imag;
break;
case 2:
res.real = -p.real;
res.imag = -p.imag;
break;
case 1:
res.imag = p.real;
res.real = -p.imag;
break;
default:
res = p;
}
return res;
}
}
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