#include <stdio.h>
#include <stdlib.h>

#define bfl(x) ((x)&~7)        // gets the floor of byte boundary
#define bcl(x) (bfl((x)+7))    // gets the ceiling of byte boundary
#define byte(x) ((x)>>3)       // gets the byte position
#define ofs(x) ((x)&7)         // gets the offset within the byte
#define getbits(pos,len) \
      ((*((unsigned long *) &data[byte(pos)])>>ofs(pos))&((1<<(len))-1))

char *data=NULL; unsigned long length=0;

/***************************************************************************/
int printb(void) {
  int i;
  for(i=0;i<length;i++) printf("%d",getbits(i,1)); printf("\n");
  return 0; }
/***************************************************************************/
int loadfile(FILE *f) {
  unsigned long x,l,i; char tmp[1000]; char *tptr;
  for(length=x=0;(l=fread(tmp,sizeof(char),1000,f))>0;x++,length+=l*8) {
    if(!(tptr=malloc(x*1000+l*sizeof(char)))) return 1;
    memcpy(tptr,data,x*1000); memcpy(&tptr[x*1000],tmp,l);
    free(data); data=tptr; }
  return 0; }
/***************************************************************************/
int savefile(FILE *f) {
  rewind(f);
  if(fwrite(data,sizeof(char),byte(bcl(length)),f)!=length) return 1;
  return 0; }
/***************************************************************************/
int chgbits(int start,int size,unsigned long val) {
  unsigned long mask=(1<<size)-1,*olay=(unsigned long *)(&data[byte(start)]);
  if(val>mask) return 1;
  val<<=ofs(start); mask<<=ofs(start); *olay=(*olay&~mask)|val;
  return 0; }
/***************************************************************************/
int insbits(int start,int size) {
  int i; char *tmp;
  if(!(tmp=malloc(byte(bcl(length+size))))) return 1;
  else length+=size;
  memcpy(tmp,data,byte(start)+1);
  for(i=bcl(start+size);i<length;i+=8) tmp[byte(i)]=getbits(i-size,8);
  free(data); data=tmp;
  chgbits(length,8-ofs(length),0);
  chgbits(start+size,8-ofs(size),getbits(start,8-ofs(size)));
  chgbits(start,size,0);
  return 0; }
/***************************************************************************/
int delbits(int start,int size) {
  int i,ofs; char *tmp;
  if(!(tmp=malloc(byte(length-size)))) return 1;
  else length-=size;
  memcpy(tmp,data,byte(bcl(start)));
  for(i=bcl(start);i<length-size;i+=8) tmp[byte(i)]=getbits(i+size,8);
  free(data); data=tmp;
  chgbits(length,8-ofs(length),0);
  chgbits(start,8-ofs(start),getbits(start+size,8-ofs(start)));
  return 0; }
/***************************************************************************/
int usage(const char *cmd) {
  int i;
  const char *opt[][2]={
    { "-L filename","Load file" },
    { "-S pos len","Show the value" },
    { "-B","Show the entire stream in binary" },
    { "-I pos len","Insert bits" },
    { "-C pos len val","Change bits to 'val'" },
    { "-D pos length","Delete bits" },
    { "-X","Exit immediately (without saving)" },
    { NULL } };
  printf("Usage:\t%s [commands]\n\n%s",cmd,
         "Bit stream editor.\n\n");
  for(printf("Options:\n"),i=0;*opt[i];i++)
    printf("\t%s\t-\t%s\n",opt[i][0],opt[i][1]);
  return 0; }
/***************************************************************************/
int main(int argc,char *argv[]) {
  int i,pos,size; unsigned long val=0; FILE *f=stdin;
  if(argc<=1) return usage(argv[0]);
  for(i=1;i<argc;i++)
    if(*argv[i]=='-')
      switch(*(argv[i]+1)) {
        case 'l': case 'L':
          loadfile(f=fopen(argv[i+1],"rb+"));
          printf("Now working with '%s'.\n",argv[i+1]); i+=1;
          break;
        case 's': case 'S':
          pos=atoi(argv[i+1]); size=atoi(argv[i+2]); val=getbits(pos,size);
          printf("Value at %d is %d (%x).\n",pos,val,val); i+=2;
          break;
        case 'b': case 'B':
          printf("Printing binary...\n",pos,val); printb();
          break;
        case 'i': case 'I':
          pos=atoi(argv[i+1]); size=atoi(argv[i+2]);
          insbits(pos,size);
          printf("Inserted %d bits at %d.\n",size,pos); i+=2;
          break;
        case 'd': case 'D':
          pos=atoi(argv[i+1]); size=atoi(argv[i+2]);
          delbits(pos,size);
          printf("Deleted %d bits at %d.\n",size,pos); i+=2;
          break;
        case 'c': case 'C':
          pos=atoi(argv[i+1]); size=atoi(argv[i+2]);
          val=atol(argv[i+3]); old=getbits(pos,size);
          chgbits(pos,size,val);
          printf("Changed %d to %d at...\n",old,val,pos); i+=3;
          break;
        case 'x': case 'X':
	  fclose(f); printf("Exiting...\n"); return 0;
    }
  printf("Saving file...");
  if(savefile(f)) printf("Couldn't save file");
  else printf("Done.\n");
  fclose(f);
  return 0;
}