IoT-Labs/Coursework/sax.h

94 lines
2.7 KiB
C

#ifndef _SAX_GUARD
#define _SAX_GUARD
#define SAX_CHAR_START 'a'
#ifndef SAX_BREAKPOINTS
#define SAX_BREAKPOINTS 4
#endif
// Could have used a 2d array for breakpoints, index by number of breakpoints
// Since the number of boundaries is known at compile-time, save these lookup calls by
// defining as as constant 1D arrays
#if SAX_BREAKPOINTS == 3
const float breakPoints[] = {-0.43, 0.43};
#elif SAX_BREAKPOINTS == 4
const float breakPoints[] = {-0.67, 0, 0.67};
#elif SAX_BREAKPOINTS == 5
const float breakPoints[] = {-0.84, -0.25, 0.25, 0.84};
#elif SAX_BREAKPOINTS == 6
const float breakPoints[] = {-0.97, -0.43, 0, 0.43, 0.97};
#elif SAX_BREAKPOINTS == 7
const float breakPoints[] = {-1.07, -0.57, -0.18, 0.18, 0.57, 1.07};
#elif SAX_BREAKPOINTS == 8
const float breakPoints[] = {-1.15, -0.67, -0.32, 0, 0.32, 0.67, 1.15};
#elif SAX_BREAKPOINTS == 9
const float breakPoints[] = {-1.22, -0.76, -0.43, -0.14, 0.14, 0.43, 0.76, 1.22};
#elif SAX_BREAKPOINTS == 10
const float breakPoints[] = {-1.28, -0.84, -0.52, -0.25, 0, 0.25, 0.52, 0.84, 1.28};
#else
#define SAX_BREAKPOINTS 4
const float breakPoints[] = {-0.67, 0, 0.67};
#endif
void
normaliseBuffer(Buffer bufferIn) // z normalise buffer for SAX
{
if(bufferIn.stats.std == 0) // error check
{
printf("Standard deviation of zero, unable to normalise\n");
return;
}
int i; // for group number
float *inputPtr = bufferIn.items; // cursor for full buffer
for(i = 0; i < bufferIn.length; i++)
{
*inputPtr = (*inputPtr - bufferIn.stats.mean) / bufferIn.stats.std;
inputPtr++; // increment both cursors
}
}
char
valueToSAXChar(float inputValue)
{
float below, above;
int i;
for(i = 0; i < SAX_BREAKPOINTS; i++)
{
if(i == 0) // first iter, is less than first breakpoint
{
if(inputValue < breakPoints[i]) return SAX_CHAR_START + i;
}
else if(i == SAX_BREAKPOINTS - 1) // last iter, is more than last breakpoint
{
if(breakPoints[i - 1] < inputValue) return SAX_CHAR_START + i;
}
else // in between check interval of two breakpoints
{
if(breakPoints[i - 1] < inputValue < breakPoints[i]) return SAX_CHAR_START + i;
}
}
return '0';
}
char* // map buffer of normalised floats into SAX chars
stringifyBuffer(Buffer bufferIn)
{
char* outputString = (char*) malloc((bufferIn.length + 1) * sizeof(char));
int i;
for(i = 0; i < bufferIn.length; i++)
{
outputString[i] = valueToSAXChar(bufferIn.items[i]);
}
outputString[bufferIn.length] = '\0'; // add null terminator
return outputString;
}
#endif