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Merge #13159: Replace FileIO's quadratic-time buffer growth algorithm with a linear-time one.

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Also fix the bz2 module, which suffered from the same problem.
This commit is contained in:
Nadeem Vawda 2011-10-13 13:38:14 +02:00
commit 72d6a13413
3 changed files with 11 additions and 27 deletions
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16
Modules/_bz2module.c
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@ -116,22 +116,14 @@ catch_bz2_error(int bzerror)
#define SMALLCHUNK BUFSIZ
#endif
#if SIZEOF_INT < 4
#define BIGCHUNK (512 * 32)
#else
#define BIGCHUNK (512 * 1024)
#endif
static int
grow_buffer(PyObject **buf)
{
/* Expand the buffer by an amount proportional to the current size,
giving us amortized linear-time behavior. Use a less-than-double
growth factor to avoid excessive allocation. */
size_t size = PyBytes_GET_SIZE(*buf);
if (size <= SMALLCHUNK)
return _PyBytes_Resize(buf, size + SMALLCHUNK);
else if (size <= BIGCHUNK)
return _PyBytes_Resize(buf, size * 2);
else
return _PyBytes_Resize(buf, size + BIGCHUNK);
return _PyBytes_Resize(buf, size + (size >> 3) + 6);
}

19
Modules/_io/fileio.c
View file

@ -43,12 +43,6 @@
#define SMALLCHUNK BUFSIZ
#endif
#if SIZEOF_INT < 4
#define BIGCHUNK (512 * 32)
#else
#define BIGCHUNK (512 * 1024)
#endif
typedef struct {
PyObject_HEAD
int fd;
@ -572,15 +566,10 @@ new_buffersize(fileio *self, size_t currentsize
}
}
#endif
if (currentsize > SMALLCHUNK) {
/* Keep doubling until we reach BIGCHUNK;
then keep adding BIGCHUNK. */
if (currentsize <= BIGCHUNK)
return currentsize + currentsize;
else
return currentsize + BIGCHUNK;
}
return currentsize + SMALLCHUNK;
/* Expand the buffer by an amount proportional to the current size,
giving us amortized linear-time behavior. Use a less-than-double
growth factor to avoid excessive allocation. */
return currentsize + (currentsize >> 3) + 6;
}
static PyObject *