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sync.c

/* sync.c   the Netwide Disassembler synchronisation processing module
 *
 * The Netwide Assembler is copyright (C) 1996 Simon Tatham and
 * Julian Hall. All rights reserved. The software is
 * redistributable under the licence given in the file "Licence"
 * distributed in the NASM archive.
 */

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

#include "sync.h"

#define SYNC_MAX 4096                /* max # of sync points */

/*
 * This lot manages the current set of sync points by means of a
 * heap (priority queue) structure.
 */

static struct Sync {
    unsigned long pos;
    unsigned long length;
} *synx;
static int nsynx;

void init_sync(void) 
{
    /*
     * I'd like to allocate an array of size SYNC_MAX, then write
     * `synx--' which would allow numbering the array from one
     * instead of zero without wasting memory. Sadly I don't trust
     * this to work in 16-bit Large model, so it's staying the way
     * it is. Btw, we don't care about freeing this array, since it
     * has to last for the duration of the program and will then be
     * auto-freed on exit. And I'm lazy ;-)
     * 
     * Speaking of 16-bit Large model, that's also the reason I'm
     * not declaring this array statically - by doing it
     * dynamically I avoid problems with the total size of DGROUP
     * in Borland C.
     */
    synx = malloc((SYNC_MAX+1) * sizeof(*synx));
    if (!synx) {
      fprintf(stderr, "ndisasm: not enough memory for sync array\n");
      exit(1);
    }
    nsynx = 0;
}

void add_sync(unsigned long pos, unsigned long length) 
{
    int i;

    if (nsynx == SYNC_MAX)
      return;                        /* can't do anything - overflow */

    nsynx++;
    synx[nsynx].pos = pos;
    synx[nsynx].length = length;

    for (i = nsynx; i > 1; i /= 2) {
      if (synx[i/2].pos > synx[i].pos) {
          struct Sync t;
          t = synx[i/2];             /* structure copy */
          synx[i/2] = synx[i];       /* structure copy again */
          synx[i] = t;         /* another structure copy */
      }
    }
}

unsigned long next_sync(unsigned long position, unsigned long *length) 
{
    while (nsynx > 0 && synx[1].pos + synx[1].length <= position) {
      int i, j;
      struct Sync t;
      t = synx[nsynx];         /* structure copy */
      synx[nsynx] = synx[1];         /* structure copy */
      synx[1] = t;                   /* ditto */

      nsynx--;

        i = 1;
      while (i*2 <= nsynx) {
          j = i*2;
          if (synx[j].pos < synx[i].pos &&
            (j+1 > nsynx || synx[j+1].pos > synx[j].pos)) {
            t = synx[j];             /* structure copy */
            synx[j] = synx[i];     /* lots of these... */
            synx[i] = t;             /* ...aren't there? */
            i = j;
          } else if (j+1 <= nsynx && synx[j+1].pos < synx[i].pos) {
            t = synx[j+1];           /* structure copy */
            synx[j+1] = synx[i];   /* structure <yawn> copy */
            synx[i] = t;             /* structure copy <zzzz....> */
            i = j+1;
          } else
            break;
      }
    }

    if (nsynx > 0) {
      if (length)
          *length = synx[1].length;
      return synx[1].pos;
    } else {
      if (length)
          *length = 0L;
      return ULONG_MAX;
    }
}

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