Code fails to execute when compiled with these flags - c

Question

My code is trying to find the entropy of a signal (stored in 'data' and 'interframe' - in the full code these would contain the signal, here I've just put in some random values). When I compile with 'gcc temp.c' it compiles and runs fine.
Output:
entropy: 40.174477
features: 0022FD06
features[0]: 40
entropy: 40
But when I compile with 'gcc -mstackrealign -msse -Os -ftree-vectorize temp.c' then it compiles, but fails to execute beyond line 48. It needs to have all four flags in order to fail - any three of them and it runs fine.
The code probably looks weird - I've chopped just the failing bits out of a much bigger program. I only have the foggiest idea of what the compiler flags do, someone else put them in (and there's usually more of them, but I worked out that these were the bad ones).
All help much appreciated!
#include <stdint.h>
#include <inttypes.h>
#include <stdio.h>
#include <math.h>
static void calc_entropy(volatile int16_t *features, const int16_t* data,
const int16_t* interframe, int frame_length);
int main()
{
int frame_length = 128;
int16_t data[128] = {1, 2, 3, 4};
int16_t interframe[128] = {1, 1, 1};
int16_t a = 0;
int16_t* features = &a;
calc_entropy(features, data, interframe, frame_length);
features += 1;
fprintf(stderr, "\nentropy: %d", a);
return 0;
}
static void calc_entropy(volatile int16_t *features, const int16_t* data,
const int16_t* interframe, int frame_length)
{
float histo[65536] = {0};
float* histo_zero = histo + 32768;
volatile float entropy = 0.0f;
int i;
for(i=0; i<frame_length; i++){
histo_zero[data[i]]++;
histo_zero[interframe[i]]++;
}
for(i=-32768; i < 32768; i++){
if(histo_zero[i])
entropy -= histo_zero[i]*logf(histo_zero[i]/(float)(frame_length*2));
}
fprintf(stderr, "\nentropy: %f", entropy);
fprintf(stderr, "\nfeatures: %p", features);
features[0] = entropy; //execution fails here
fprintf(stderr, "\nfeatures[0]: %d", features[0]);
}
Edit: I'm using gcc 4.5.2, with x86 architecture. Also, if I compile and run it on VirtualBox running ubuntu (gcc -lm -mstackrealign -msse -Os -ftree-vectorize temp.c) it executes correctly.
Edit2: I get
entropy: 40.174477
features: 00000000
and then a message from windows telling me that the program has stopped running.
Edit3: In the five months since I originally posted the question I've updated to gcc 4.7.0, and the code now runs fine. I went back to gcc 4.5.2, and it failed. Still don't know why!

Answer 1

ottavio#magritte:/tmp$ gcc x.c -o x -lm -mstackrealign -msse -Os -ftree-vectorize
ottavio#magritte:/tmp$ ./x
entropy: 40.174477
features: 0x7fff5fe151ce
features[0]: 40
entropy: 40
ottavio#magritte;/tmp$ gcc x.c -o x -lm
ottavio#magritte:/tmp$ ./x
entropy: 40.174477
features: 0x7fffd7eff73e
features[0]: 40
entropy: 40
ottavio#magritte:/tmp$
So, what's wrong with it? gcc 4.6.1 and x86_64 architecture.

Answer 2

It seems to be running here as well, and the only thing I see that might be funky is that you are taking a 16 bit value (features[0]) and converting a 32 bit float (entropy)
features[0] = entropy; //execution fails here
into that value, which of course will shave it off.
It shouldn't matter, but for the heck of it, see if it makes any difference if change your int16_t values to int32_t values.