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#include "medfilter.h" /* median, filter, usage */
void usage(void) {
fprintf(stderr, "Usage: medfilter WINDOW\n"); /* argv[0] may be better */
exit(EXIT_FAILURE);
}
int main(int argc, char** argv) {
if(argc != 2)
usage();
uint32_t wndsz;
sscanf(argv[1], "%"SCNu32, &wndsz);
if(wndsz % 2 == 0 || wndsz == 0) {
fprintf(stderr, "Window must be odd and positive\n");
exit(2);
}
filter(wndsz, stdin, stdout);
return 0;
}
void filter(uint32_t wndsz, FILE* in, FILE* out) {
/* (wndsz-1)/2 */
uint32_t halfwndsz = wndsz >> 1;
/* buffers for signal and window */
int32_t* sigbuf;
int32_t* wndbuf;
fprintf(stderr, "Allocating memory for window buffer (%"SCNu32" * sizeof(int32_t) bytes)...\n", wndsz);
wndbuf = (int32_t*)calloc(sizeof(int32_t), wndsz);
size_t sigbufsz = (wndsz > MAX_BUFFER ? wndsz+halfwndsz : MAX_BUFFER);
fprintf(stderr, "Allocating memory for signal buffer (%"SCNu32" * sizeof(int32_t) bytes)...\n", wndsz);
sigbuf = (int32_t*)calloc(sizeof(int32_t), sigbufsz);
/*
sigbuf = [ x x x x x x n n n n n n n n n ]
------------- -------------------
prev halfwnd new part of signal
*/
size_t n;
int c;
/* pointer to first element of part of signal */
int32_t* first_sigel = sigbuf+halfwndsz;
/* pointer to last element of part of signal */
int32_t* last_sigel;
/* iterators */
int32_t* i;
int32_t* j;
/* median of window */
int32_t m;
/* fill ``prev halfwnd'' by first element of signal at first iteration */
char first_iteration = 0;
while((n = fread(first_sigel, sizeof(int32_t), sigbufsz-halfwndsz, in)) > 0) {
if(n < wndsz && !first_iteration) {
fprintf(stderr, "Window size more than input length (%"SCNu32" > %zu)\n", wndsz, n);
exit(2);
}
#ifdef DEBUG
uint32_t l1;
fprintf(stderr, "sigbuf in = {");
for(l1 = 0; l1 < sigbufsz; l1++)
fprintf(stderr, "%"SCNi32",", sigbuf[l1]);
fprintf(stderr, "}\n");
#endif
last_sigel = first_sigel + n - 1;
for(i = first_sigel; i != last_sigel + 1; i++) {
if(!first_iteration) {
for(j = i - halfwndsz; j != i; j++) {
(*j) = *i;
}
first_iteration = 1;
}
c = 0;
for(j = i - halfwndsz; j != i + halfwndsz + 1; j++) {
if(j > last_sigel)
wndbuf[c++] = *last_sigel;
else
wndbuf[c++] = *j;
}
#ifdef DEBUG
fprintf(stderr, "arr for %"SCNi32" (len: %"SCNi32"): { ", *i, wndsz);
for(l1 = 0; l1 < wndsz; l1++)
fprintf(stderr, "%"SCNi32", ", wndbuf[l1]);
#endif
m = medium(wndbuf, wndsz);
#ifdef DEBUG
fprintf(stderr,"}, median: %"SCNi32"\n", m);
#endif
fwrite(&m, sizeof(int32_t), 1, out);
}
/* filling beginning of sigbuf by last N elements of signal, where N = halfwnd */
c = 0;
for(i = last_sigel - halfwndsz + 1; i != last_sigel + 1; i++)
sigbuf[c++] = *i;
#ifdef DEBUG
fprintf(stderr, "sigbuf out = {");
for(l1 = 0; l1 < sigbufsz; l1++)
fprintf(stderr, "%"SCNi32",", sigbuf[l1]);
fprintf(stderr, "}\n");
#endif
}
free(sigbuf);
free(wndbuf);
}
/* Fast, destructive median selection, credit to Nicolas Devillard for
the original C implementation. */
#define SWAP(a,b) { register int32_t t=(a);(a)=(b);(b)=t; }
int32_t medium(int32_t* arr, uint32_t n)
{
long low, high;
long median;
long middle, ll, hh;
low = 0;
high = n-1;
median = (low + high) / 2;
for (;;)
{
/* One element only */
if (high <= low)
return arr[median];
/* Two elements only */
if (high == low + 1)
{
if (arr[low] > arr[high])
SWAP(arr[low], arr[high]);
return arr[median];
}
/* Find median of low, middle and high items; swap to low position */
middle = (low + high) / 2;
if (arr[middle] > arr[high])
SWAP(arr[middle], arr[high]);
if (arr[low] > arr[high])
SWAP(arr[low], arr[high]);
if (arr[middle] > arr[low])
SWAP(arr[middle], arr[low]);
/* Swap low item (now in position middle) into position (low+1) */
SWAP(arr[middle], arr[low+1]);
/* Work from each end towards middle, swapping items when stuck */
ll = low + 1;
hh = high;
for (;;)
{
do
ll++;
while (arr[low] > arr[ll]);
do
hh--;
while (arr[hh] > arr[low]);
if (hh < ll)
break;
SWAP(arr[ll], arr[hh]);
}
/* Swap middle item (in position low) back into correct position */
SWAP(arr[low], arr[hh]);
/* Reset active partition */
if (hh <= median)
low = ll;
if (hh >= median)
high = hh - 1;
}
}
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