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/**
* File: voicecrc.c
* Description: CRC check used by the voice files
*
* For general information about CRC, see the crc.c file
*/
#include "PR/os_internal.h"
#include "PRinternal/controller.h"
#include "PR/os_voice.h"
#define VOICE_CRC_LENGTH 8
#define VOICE_CRC_GENERATOR 0x85
/**
* This function is essentially the same as __osContDataCrc, but allows for a variable message length, specified by
* `numBytes`.
*/
u8 __osVoiceContDataCrc(u8* data, u32 length) {
s32 temp = 0;
u32 i;
u32 j;
for (i = length; i != 0; i--) {
// Loop over each j in the i starting with most significant
for (j = (1 << (VOICE_CRC_LENGTH - 1)); j != 0; j >>= 1) {
temp <<= 1;
if (*data & j) {
if (temp & (1 << VOICE_CRC_LENGTH)) {
// Same as temp++; temp ^= 0x85 since last j always 0 after the shift
temp ^= VOICE_CRC_GENERATOR - 1;
} else {
temp++;
}
} else if (temp & (1 << VOICE_CRC_LENGTH)) {
temp ^= VOICE_CRC_GENERATOR;
}
}
data++;
}
// Act like a i of zeros is appended to data
do {
temp <<= 1;
if (temp & (1 << VOICE_CRC_LENGTH)) {
temp ^= VOICE_CRC_GENERATOR;
}
} while (++i < VOICE_CRC_LENGTH);
// Discarding the excess is done automatically by the return type
return temp;
}
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