dialogus/randomizer.c at main · OpenResearchInstitute/dialogus · GitHub

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#include "numerology.h"
#include "randomizer.h"

#if 0
static uint8_t old_randomization_sequence[OVP_SINGLE_FRAME_SIZE] = {
	163, 129,  92, 196, 201,   8,  14,  83, 204, 161,
	251,  41, 158,  79,  22, 224, 151,  78,  43,  87,
	 18, 167,  63, 194,  77, 107,  15,   8,  48,  70,
	 17,  86,  13,  26,  19, 231,  80, 151,  97, 243,
	190, 227, 153, 176, 100,  57,  34,  44, 240,   9,

	225, 134, 207, 115,  89, 194,  92, 142, 227, 215,
	 63, 112, 212,  39, 194, 224, 129, 146, 218, 252,
	202,  90, 128,  66, 131,  21,  15, 162, 158,  21,
	156, 139, 219, 164,  70,  28,  16, 159, 179,  71,
	108,  94,  21,  18,  31, 173,  56,  61,   3, 186,

	144, 141, 190, 211, 101,  35,  50, 184, 171,  16,
	 98, 126, 198,  38, 124,  19, 201, 101,  61,  21,
	 21, 237,  53, 244,  87, 245,  88,  17, 157, 142,
	232,  52, 201,  89
};
#endif // 0

#if 0
// Python code to generate the CCSDS randomization sequence
// as defined in CCSDS 101.0-B-3, h(x) = x^8 + x^7 + x^5 + x^3 + 1
//
// lfsr = 0xff
// for byte_index in range(0,134):
//     value = 0
//     for bit_index in range(0,8):
//         value = (value << 1) | (lfsr & 0x01)
//         feedback = bool(lfsr & 0x01) ^ bool(lfsr & 0x08) ^ bool(lfsr & 0x20) ^ bool(lfsr & 0x80)
//         lfsr = (lfsr >> 1) & 0x7f
//         if feedback:
//             lfsr = lfsr | 0x80
//     print(f"0x{value:02x}, ", end="")

static uint8_t ccsds_101_0_b_3_randomization_sequence[OVP_SINGLE_FRAME_SIZE] = {
	0xff, 0x48, 0x0e, 0xc0, 0x9a, 0x0d, 0x70, 0xbc, 0x8e, 0x2c,
	0x93, 0xad, 0xa7, 0xb7, 0x46, 0xce, 0x5a, 0x97, 0x7d, 0xcc,
	0x32, 0xa2, 0xbf, 0x3e, 0x0a, 0x10, 0xf1, 0x88, 0x94, 0xcd,
	0xea, 0xb1, 0xfe, 0x90, 0x1d, 0x81, 0x34, 0x1a, 0xe1, 0x79,
	0x1c, 0x59, 0x27, 0x5b, 0x4f, 0x6e, 0x8d, 0x9c, 0xb5, 0x2e,

	0xfb, 0x98, 0x65, 0x45, 0x7e, 0x7c, 0x14, 0x21, 0xe3, 0x11,
	0x29, 0x9b, 0xd5, 0x63, 0xfd, 0x20, 0x3b, 0x02, 0x68, 0x35,
	0xc2, 0xf2, 0x38, 0xb2, 0x4e, 0xb6, 0x9e, 0xdd, 0x1b, 0x39,
	0x6a, 0x5d, 0xf7, 0x30, 0xca, 0x8a, 0xfc, 0xf8, 0x28, 0x43,
	0xc6, 0x22, 0x53, 0x37, 0xaa, 0xc7, 0xfa, 0x40, 0x76, 0x04,

	0xd0, 0x6b, 0x85, 0xe4, 0x71, 0x64, 0x9d, 0x6d, 0x3d, 0xba,
	0x36, 0x72, 0xd4, 0xbb, 0xee, 0x61, 0x95, 0x15, 0xf9, 0xf0,
	0x50, 0x87, 0x8c, 0x44, 0xa6, 0x6f, 0x55, 0x8f, 0xf4, 0x80,
	0xec, 0x09, 0xa0, 0xd7
};
#endif // 0

static uint8_t ovp_randomization_sequence[OVP_SINGLE_FRAME_SIZE] = {
	0xff, 0x1a, 0xaf, 0x66, 0x52, 0x23, 0x1e, 0x10, 0xa0, 0xf9,
	0xfa, 0x8a, 0x98, 0x67, 0x7d, 0xd2, 0xb4, 0xe6, 0xc5, 0xdb,
	0xcb, 0x6b, 0x92, 0x68, 0xe2, 0x7a, 0x1d, 0x60, 0xb2, 0x06,
	0xe0, 0x25, 0xfe, 0x35, 0x5e, 0xcc, 0xa4, 0x46, 0x3c, 0x21,
	0x41, 0xf3, 0xf5, 0x15, 0x30, 0xce, 0xfb, 0xa5, 0x69, 0xcd,

	0x8b, 0xb7, 0x96, 0xd7, 0x24, 0xd1, 0xc4, 0xf4, 0x3a, 0xc1,
	0x64, 0x0d, 0xc0, 0x4b, 0xfc, 0x6a, 0xbd, 0x99, 0x48, 0x8c,
	0x78, 0x42, 0x83, 0xe7, 0xea, 0x2a, 0x61, 0x9d, 0xf7, 0x4a,
	0xd3, 0x9b, 0x17, 0x6f, 0x2d, 0xae, 0x49, 0xa3, 0x89, 0xe8,
	0x75, 0x82, 0xc8, 0x1b, 0x80, 0x97, 0xf8, 0xd5, 0x7b, 0x32,

	0x91, 0x18, 0xf0, 0x85, 0x07, 0xcf, 0xd4, 0x54, 0xc3, 0x3b,
	0xee, 0x95, 0xa7, 0x36, 0x2e, 0xde, 0x5b, 0x5c, 0x93, 0x47,
	0x13, 0xd0, 0xeb, 0x05, 0x90, 0x37, 0x01, 0x2f, 0xf1, 0xaa,
	0xf6, 0x65, 0x22, 0x31
};

// apply or remove randomization, in place, to reduce spectral features of the data
void randomize_ovp_frame(uint8_t *buf) {
	for (int i=0; i < OVP_SINGLE_FRAME_SIZE; i++) {
		buf[i] ^= ovp_randomization_sequence[i];
	}
}