memory inefficiency in builtin-commit-tree.c - add_buffer() - in git version 1.5.2

["Tim Stewart" <tim.j.stewart@xxxxxxxxx>]

The function init_buffer allocates 16,384 bytes.  This function then
sets the size of the buffer at 0 bytes.

Then when add_buffer is called, it calculates how much memory the
added bytes will take up here:

       alloc = (size + 32767) & ~32767;

Since size is 0, alloc will be 0.  So the next line:

        if (newsize > alloc) {

will always evaluate to true (unless newsize is 0) and then the
function reallocs the buffer at twice it's current size.

This all but guarantees that the memory allocated in init_buffer will
be realloc'ed.

Here is the code for your reference:

static void init_buffer(char **bufp, unsigned int *sizep)
{
       *bufp = xmalloc(BLOCKING);
       *sizep = 0;
}

static void add_buffer(char **bufp, unsigned int *sizep, const char *fmt, ...)
{
       char one_line[2048];
       va_list args;
       int len;
       unsigned long alloc, size, newsize;
       char *buf;

       va_start(args, fmt);
       len = vsnprintf(one_line, sizeof(one_line), fmt, args);
       va_end(args);
       size = *sizep;
       newsize = size + len + 1;
       alloc = (size + 32767) & ~32767;
       buf = *bufp;
       if (newsize > alloc) {
               alloc = (newsize + 32767) & ~32767;
               buf = xrealloc(buf, alloc);
               *bufp = buf;
       }
       *sizep = newsize - 1;
       memcpy(buf + size, one_line, len);
}
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