Implement the other easy thing: repr() of a float now uses %.17g,
while str() uses %.12g as before.
diff --git a/Objects/floatobject.c b/Objects/floatobject.c
index cb5d9e3..557a641 100644
--- a/Objects/floatobject.c
+++ b/Objects/floatobject.c
@@ -243,9 +243,10 @@
/* Methods */
void
-PyFloat_AsString(buf, v)
+PyFloat_AsStringEx(buf, v, precision)
char *buf;
PyFloatObject *v;
+ int precision;
{
register char *cp;
/* Subroutine for float_repr and float_print.
@@ -253,7 +254,7 @@
i.e., they should contain a decimal point or an exponent.
However, %g may print the number as an integer;
in such cases, we append ".0" to the string. */
- sprintf(buf, "%.12g", v->ob_fval);
+ sprintf(buf, "%.*g", precision, v->ob_fval);
cp = buf;
if (*cp == '-')
cp++;
@@ -270,6 +271,31 @@
}
}
+/* Precisions used by repr() and str(), respectively.
+
+ The repr() precision (17 significant decimal digits) is the minimal number
+ that is guaranteed to have enough precision so that if the number is read
+ back in the exact same binary value is recreated. This is true for IEEE
+ floating point by design, and also happens to work for all other modern
+ hardware.
+
+ The str() precision is chosen so that in most cases, the rounding noise
+ created by various operations is suppressed, while giving plenty of
+ precision for practical use.
+
+*/
+
+#define PREC_REPR 17
+#define PREC_STR 12
+
+void
+PyFloat_AsString(buf, v)
+ char *buf;
+ PyFloatObject *v;
+{
+ PyFloat_AsStringEx(buf, v, PREC_STR);
+}
+
/* ARGSUSED */
static int
float_print(v, fp, flags)
@@ -278,7 +304,7 @@
int flags; /* Not used but required by interface */
{
char buf[100];
- PyFloat_AsString(buf, v);
+ PyFloat_AsStringEx(buf, v, flags&Py_PRINT_RAW ? PREC_STR : PREC_REPR);
fputs(buf, fp);
return 0;
}
@@ -288,7 +314,16 @@
PyFloatObject *v;
{
char buf[100];
- PyFloat_AsString(buf, v);
+ PyFloat_AsStringEx(buf, v, PREC_REPR);
+ return PyString_FromString(buf);
+}
+
+static PyObject *
+float_str(v)
+ PyFloatObject *v;
+{
+ char buf[100];
+ PyFloat_AsStringEx(buf, v, PREC_STR);
return PyString_FromString(buf);
}
@@ -673,11 +708,13 @@
0, /*tp_getattr*/
0, /*tp_setattr*/
(cmpfunc)float_compare, /*tp_compare*/
- (reprfunc)float_repr, /*tp_repr*/
+ (reprfunc)float_repr, /*tp_repr*/
&float_as_number, /*tp_as_number*/
0, /*tp_as_sequence*/
0, /*tp_as_mapping*/
- (hashfunc)float_hash, /*tp_hash*/
+ (hashfunc)float_hash, /*tp_hash*/
+ 0, /*tp_call*/
+ (reprfunc)float_str, /*tp_str*/
};
void