[Python-checkins] bpo-47005: Improve performance of bytearray_repeat and bytearray_irepeat (GH-31856)

Thu Mar 17 19:10:56 EDT 2022

https://github.com/python/cpython/commit/ac8308d3eaf2526318c1bbf13d4a214fd24605d2
commit: ac8308d3eaf2526318c1bbf13d4a214fd24605d2
branch: main
author: Pieter Eendebak <pieter.eendebak at gmail.com>
committer: sweeneyde <36520290+sweeneyde at users.noreply.github.com>
date: 2022年03月17日T19:10:36-04:00
summary:
bpo-47005: Improve performance of bytearray_repeat and bytearray_irepeat (GH-31856)
files:
A Misc/NEWS.d/next/Core and Builtins/2022-03-13-21-04-20.bpo-47005.OHBfCc.rst
M Objects/bytearrayobject.c

diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-03-13-21-04-20.bpo-47005.OHBfCc.rst b/Misc/NEWS.d/next/Core and Builtins/2022-03-13-21-04-20.bpo-47005.OHBfCc.rst
new file mode 100644
index 0000000000000..bf8a4f92a1e7f
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-03-13-21-04-20.bpo-47005.OHBfCc.rst	
@@ -0,0 +1 @@
+Improve performance of ``bytearray_repeat`` and ``bytearray_irepeat`` by reducing the number of invocations of ``memcpy``.
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index 3493ff046ae13..ba2d347dbd7a8 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -335,9 +335,19 @@ bytearray_repeat(PyByteArrayObject *self, Py_ssize_t count)
 if (mysize == 1)
 memset(result->ob_bytes, buf[0], size);
 else {
- Py_ssize_t i;
- for (i = 0; i < count; i++)
- memcpy(result->ob_bytes + i*mysize, buf, mysize);
+ Py_ssize_t i, j;
+
+ i = 0;
+ if (i < size) {
+ memcpy(result->ob_bytes, buf, mysize);
+ i = mysize;
+ }
+ // repeatedly double the number of bytes copied
+ while (i < size) {
+ j = Py_MIN(i, size - i);
+ memcpy(result->ob_bytes + i, result->ob_bytes, j);
+ i += j;
+ }
 }
 }
 return (PyObject *)result;
@@ -363,9 +373,15 @@ bytearray_irepeat(PyByteArrayObject *self, Py_ssize_t count)
 if (mysize == 1)
 memset(buf, buf[0], size);
 else {
- Py_ssize_t i;
- for (i = 1; i < count; i++)
- memcpy(buf + i*mysize, buf, mysize);
+ Py_ssize_t i, j;
+
+ i = mysize;
+ // repeatedly double the number of bytes copied
+ while (i < size) {
+ j = Py_MIN(i, size - i);
+ memcpy(buf + i, buf, j);
+ i += j;
+ }
 }
 
 Py_INCREF(self);
