index.c

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/*
    index: frame index data structure and functions

    copyright 2007-8 by the mpg123 project - free software under the terms of the LGPL 2.1
    see COPYING and AUTHORS files in distribution or http://mpg123.org
    initially written by Thomas Orgis
*/

#include "index.h"
#include "debug.h"

/* The next expected frame offset, one step ahead. */
static off_t fi_next(struct frame_index *fi)
{
    return (off_t)fi->fill*fi->step;
}

/* Shrink down the used index to the half.
   Be careful with size = 1 ... there's no shrinking possible there. */
static void fi_shrink(struct frame_index *fi)
{
    if(fi->fill < 2) return; /* Won't shrink below 1. */
    else
    { /* Double the step, half the fill. Should work as well for fill%2 = 1 */
        size_t c;
        debug2("shrink index with fill %lu and step %lu", (unsigned long)fi->fill, (unsigned long)fi->step);
        fi->step *= 2;
        fi->fill /= 2;
        /* Move the data down. */
        for(c = 0; c < fi->fill; ++c)
        fi->data[c] = fi->data[2*c];
    }

    fi->next = fi_next(fi);
}

void fi_init(struct frame_index *fi)
{
    fi->data = NULL;
    fi->step = 1;
    fi->fill = 0;
    fi->size = 0;
    fi->grow_size = 0;
    fi->next = fi_next(fi);
}

void fi_exit(struct frame_index *fi)
{
    debug2("fi_exit: %p and %lu", (void*)fi->data, (unsigned long)fi->size);
    if(fi->size && fi->data != NULL) free(fi->data);

    fi_init(fi); /* Be prepared for further fun, still. */
}

int fi_resize(struct frame_index *fi, size_t newsize)
{
    off_t *newdata = NULL;
    if(newsize == fi->size) return 0;

    if(newsize > 0 && newsize < fi->size)
    { /* When we reduce buffer size a bit, shrink stuff. */
        while(fi->fill > newsize){ fi_shrink(fi); }
    }

    newdata = safe_realloc(fi->data, newsize*sizeof(off_t));
    if(newsize == 0 || newdata != NULL)
    {
        fi->data = newdata;
        fi->size = newsize;
        if(fi->fill > fi->size) fi->fill = fi->size;

        fi->next = fi_next(fi);
        debug2("new index of size %lu at %p", (unsigned long)fi->size, (void*)fi->data);
        return 0;
    }
    else
    {
        error("failed to resize index!");
        return -1;
    }
}

void fi_add(struct frame_index *fi, off_t pos)
{
    debug3("wanting to add to fill %lu, step %lu, size %lu", (unsigned long)fi->fill, (unsigned long)fi->step, (unsigned long)fi->size);
    if(fi->fill == fi->size)
    { /* Index is full, we need to shrink... or grow. */
        /* Store the current frame number to check later if we still want it. */
        off_t framenum = fi->fill*fi->step;
        /* If we want not / cannot grow, we shrink. */  
        if( !(fi->grow_size && fi_resize(fi, fi->size+fi->grow_size)==0) )
        fi_shrink(fi);

        /* Now check if we still want to add this frame (could be that not, because of changed step). */
        if(fi->next != framenum) return;
    }
    /* When we are here, we want that frame. */
    if(fi->fill < fi->size) /* safeguard for size=1, or just generally */
    {
        debug1("adding to index at %p", (void*)(fi->data+fi->fill));
        fi->data[fi->fill] = pos;
        ++fi->fill;
        fi->next = fi_next(fi);
        debug3("added pos %li to index with fill %lu and step %lu", (long) pos, (unsigned long)fi->fill, (unsigned long)fi->step);
    }
}

int fi_set(struct frame_index *fi, off_t *offsets, off_t step, size_t fill)
{
    if(fi_resize(fi, fill) == -1) return -1;
    fi->step = step;
    if(offsets != NULL)
    {
        memcpy(fi->data, offsets, fill*sizeof(off_t));
        fi->fill = fill;
    }
    else
    {
        /* allocation only, no entries in index yet */
        fi->fill = 0;
    }
    fi->next = fi_next(fi);
    debug3("set new index of fill %lu, size %lu at %p",
    (unsigned long)fi->fill, (unsigned long)fi->size, (void*)fi->data);
    return 0;
}

void fi_reset(struct frame_index *fi)
{
    debug1("reset with size %"SIZE_P, (size_p)fi->size);
    fi->fill = 0;
    fi->step = 1;
    fi->next = fi_next(fi);
}