Grow the string buffer at a mildly exponential rate for the getc version

of get_line.  This makes test_bufio finish in 1.7 seconds instead of 57
seconds on my machine (with Py_DEBUG defined).

Also, rename the local variables n1 and n2 to used_v_size and
total_v_size.

diff --git a/Objects/fileobject.c b/Objects/fileobject.c
index 6a82cce7030c6a1a70a21a23a531e21e86845eeb..ebe0d2993c0fdcd4f6072e934889befd2ebe6c59 100644 (file)
--- a/Objects/fileobject.c
+++ b/Objects/fileobject.c
@@ -937,19 +937,21 @@ get_line(PyFileObject *f, int n)
        FILE *fp = f->f_fp;
        int c;
        char *buf, *end;
-       size_t n1, n2;
+       size_t total_v_size;    /* total # of slots in buffer */
+       size_t used_v_size;     /* # used slots in buffer */
+       size_t increment;       /* amount to increment the buffer */
        PyObject *v;
 
 #ifdef USE_FGETS_IN_GETLINE
        if (n <= 0)
                return getline_via_fgets(fp);
 #endif
-       n2 = n > 0 ? n : 100;
-       v = PyString_FromStringAndSize((char *)NULL, n2);
+       total_v_size = n > 0 ? n : 100;
+       v = PyString_FromStringAndSize((char *)NULL, total_v_size);
        if (v == NULL)
                return NULL;
        buf = BUF(v);
-       end = buf + n2;
+       end = buf + total_v_size;
 
        for (;;) {
                Py_BEGIN_ALLOW_THREADS
@@ -979,23 +981,24 @@ get_line(PyFileObject *f, int n)
                /* Must be because buf == end */
                if (n > 0)
                        break;
-               n1 = n2;
-               n2 += 1000;
-               if (n2 > INT_MAX) {
+               used_v_size = total_v_size;
+               increment = total_v_size >> 2; /* mild exponential growth */
+               total_v_size += increment;
+               if (total_v_size > INT_MAX) {
                        PyErr_SetString(PyExc_OverflowError,
                            "line is longer than a Python string can hold");
                        Py_DECREF(v);
                        return NULL;
                }
-               if (_PyString_Resize(&v, n2) < 0)
+               if (_PyString_Resize(&v, total_v_size) < 0)
                        return NULL;
-               buf = BUF(v) + n1;
-               end = BUF(v) + n2;
+               buf = BUF(v) + used_v_size;
+               end = BUF(v) + total_v_size;
        }
 
-       n1 = buf - BUF(v);
-       if (n1 != n2)
-               _PyString_Resize(&v, n1);
+       used_v_size = buf - BUF(v);
+       if (used_v_size != total_v_size)
+               _PyString_Resize(&v, used_v_size);
        return v;
 }