bdiff: don't check border condition in loop
This is pretty much a copy of d500ddae7494, just to a different loop.
The condition `p == plast` (`plast == a + len - 1`) was only true on
the final iteration of the loop. So it was wasteful to check for it
on every iteration. We decrease the iteration count by 1 and add an
explicit check for `p == plast` after the loop.
Again, we see modest wins.
From the mozilla-unified repository:
$ perfbdiff -m 3041e4d59df2
! wall 0.035502 comb 0.040000 user 0.040000 sys 0.000000 (best of 100)
! wall 0.030480 comb 0.030000 user 0.030000 sys 0.000000 (best of 100)
$ perfbdiff 0e9928989e9c --alldata --count 100
! wall 4.097394 comb 4.100000 user 4.100000 sys 0.000000 (best of 3)
! wall 3.597798 comb 3.600000 user 3.600000 sys 0.000000 (best of 3)
The 2nd example throws a total of ~3.3GB of data at bdiff. This
change increases the throughput from ~811 MB/s to ~924 MB/s.
/**
* Copyright (c) 2016-present, Gregory Szorc
* All rights reserved.
*
* This software may be modified and distributed under the terms
* of the BSD license. See the LICENSE file for details.
*/
/* A Python C extension for Zstandard. */
#include "python-zstandard.h"
PyObject *ZstdError;
PyDoc_STRVAR(estimate_compression_context_size__doc__,
"estimate_compression_context_size(compression_parameters)\n"
"\n"
"Give the amount of memory allocated for a compression context given a\n"
"CompressionParameters instance");
PyDoc_STRVAR(estimate_decompression_context_size__doc__,
"estimate_decompression_context_size()\n"
"\n"
"Estimate the amount of memory allocated to a decompression context.\n"
);
static PyObject* estimate_decompression_context_size(PyObject* self) {
return PyLong_FromSize_t(ZSTD_estimateDCtxSize());
}
PyDoc_STRVAR(get_compression_parameters__doc__,
"get_compression_parameters(compression_level[, source_size[, dict_size]])\n"
"\n"
"Obtains a ``CompressionParameters`` instance from a compression level and\n"
"optional input size and dictionary size");
PyDoc_STRVAR(train_dictionary__doc__,
"train_dictionary(dict_size, samples)\n"
"\n"
"Train a dictionary from sample data.\n"
"\n"
"A compression dictionary of size ``dict_size`` will be created from the\n"
"iterable of samples provided by ``samples``.\n"
"\n"
"The raw dictionary content will be returned\n");
static char zstd_doc[] = "Interface to zstandard";
static PyMethodDef zstd_methods[] = {
{ "estimate_compression_context_size", (PyCFunction)estimate_compression_context_size,
METH_VARARGS, estimate_compression_context_size__doc__ },
{ "estimate_decompression_context_size", (PyCFunction)estimate_decompression_context_size,
METH_NOARGS, estimate_decompression_context_size__doc__ },
{ "get_compression_parameters", (PyCFunction)get_compression_parameters,
METH_VARARGS, get_compression_parameters__doc__ },
{ "train_dictionary", (PyCFunction)train_dictionary,
METH_VARARGS | METH_KEYWORDS, train_dictionary__doc__ },
{ NULL, NULL }
};
void compressobj_module_init(PyObject* mod);
void compressor_module_init(PyObject* mod);
void compressionparams_module_init(PyObject* mod);
void constants_module_init(PyObject* mod);
void dictparams_module_init(PyObject* mod);
void compressiondict_module_init(PyObject* mod);
void compressionwriter_module_init(PyObject* mod);
void compressoriterator_module_init(PyObject* mod);
void decompressor_module_init(PyObject* mod);
void decompressobj_module_init(PyObject* mod);
void decompressionwriter_module_init(PyObject* mod);
void decompressoriterator_module_init(PyObject* mod);
void zstd_module_init(PyObject* m) {
compressionparams_module_init(m);
dictparams_module_init(m);
compressiondict_module_init(m);
compressobj_module_init(m);
compressor_module_init(m);
compressionwriter_module_init(m);
compressoriterator_module_init(m);
constants_module_init(m);
decompressor_module_init(m);
decompressobj_module_init(m);
decompressionwriter_module_init(m);
decompressoriterator_module_init(m);
}
#if PY_MAJOR_VERSION >= 3
static struct PyModuleDef zstd_module = {
PyModuleDef_HEAD_INIT,
"zstd",
zstd_doc,
-1,
zstd_methods
};
PyMODINIT_FUNC PyInit_zstd(void) {
PyObject *m = PyModule_Create(&zstd_module);
if (m) {
zstd_module_init(m);
}
return m;
}
#else
PyMODINIT_FUNC initzstd(void) {
PyObject *m = Py_InitModule3("zstd", zstd_methods, zstd_doc);
if (m) {
zstd_module_init(m);
}
}
#endif