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-rw-r--r--generic/tclUtil.c126
1 files changed, 87 insertions, 39 deletions
diff --git a/generic/tclUtil.c b/generic/tclUtil.c
index ee17166..ff2fb6f 100644
--- a/generic/tclUtil.c
+++ b/generic/tclUtil.c
@@ -11,7 +11,7 @@
* See the file "license.terms" for information on usage and redistribution of
* this file, and for a DISCLAIMER OF ALL WARRANTIES.
*
- * RCS: @(#) $Id: tclUtil.c,v 1.97.2.9 2010/12/03 22:27:44 hobbs Exp $
+ * RCS: @(#) $Id: tclUtil.c,v 1.97.2.10 2011/01/15 19:07:01 kennykb Exp $
*/
#include "tclInt.h"
@@ -2273,7 +2273,47 @@ Tcl_PrintDouble(
digits = TclDoubleDigits(value, -1, TCL_DD_SHORTEST,
&exponent, &signum, &end);
} else {
- digits = TclDoubleDigits(value, *precisionPtr, TCL_DD_E_FORMAT,
+ /*
+ * There are at least two possible interpretations for tcl_precision.
+ *
+ * The first is, "choose the decimal representation having
+ * $tcl_precision digits of significance that is nearest to the
+ * given number, breaking ties by rounding to even, and then
+ * trimming trailing zeros." This gives the greatest possible
+ * precision in the decimal string, but offers the anomaly that
+ * [expr 0.1] will be "0.10000000000000001".
+ *
+ * The second is "choose the decimal representation having at
+ * most $tcl_precision digits of significance that is nearest
+ * to the given number. If no such representation converts
+ * exactly to the given number, choose the one that is closest,
+ * breaking ties by rounding to even. If more than one such
+ * representation converts exactly to the given number, choose
+ * the shortest, breaking ties in favour of the nearest, breaking
+ * remaining ties in favour of the one ending in an even digit."
+ *
+ * Tcl 8.4 implements the first of these, which gives rise to
+ * anomalies in formatting:
+ *
+ * % expr 0.1
+ * 0.10000000000000001
+ * % expr 0.01
+ * 0.01
+ * % expr 1e-7
+ * 9.9999999999999995e-08
+ *
+ * For human readability, it appears better to choose the second rule,
+ * and let [expr 0.1] return 0.1. But for 8.4 compatibility, we
+ * prefer the first (the recommended zero value for tcl_precision
+ * avoids the problem entirely).
+ *
+ * Uncomment TCL_DD_SHORTEN_FLAG in the next call to prefer the
+ * method that allows floating point values to be shortened if
+ * it can be done without loss of precision.
+ */
+
+ digits = TclDoubleDigits(value, *precisionPtr,
+ TCL_DD_E_FORMAT /* | TCL_DD_SHORTEN_FLAG */,
&exponent, &signum, &end);
}
if (signum) {
@@ -2281,51 +2321,59 @@ Tcl_PrintDouble(
}
p = digits;
if (exponent < -4 || exponent > 16) {
- /*
- * E format for numbers < 1e-3 or >= 1e17.
- */
-
- *dst++ = *p++;
- c = *p;
- if (c != '\0') {
- *dst++ = '.';
- while (c != '\0') {
- *dst++ = c;
- c = *++p;
- }
+ /*
+ * E format for numbers < 1e-3 or >= 1e17.
+ */
+
+ *dst++ = *p++;
+ c = *p;
+ if (c != '\0') {
+ *dst++ = '.';
+ while (c != '\0') {
+ *dst++ = c;
+ c = *++p;
}
- sprintf(dst, "e%+d", exponent);
+ }
+ /*
+ * Tcl 8.4 appears to format with at least a two-digit exponent; \
+ * preserve that behaviour when tcl_precision != 0
+ */
+ if (*precisionPtr == 0) {
+ sprintf(dst, "e%+d", exponent);
} else {
- /*
- * F format for others.
- */
-
+ sprintf(dst, "e%+03d", exponent);
+ }
+ } else {
+ /*
+ * F format for others.
+ */
+
if (exponent < 0) {
- *dst++ = '0';
- }
- c = *p;
+ *dst++ = '0';
+ }
+ c = *p;
while (exponent-- >= 0) {
- if (c != '\0') {
- *dst++ = c;
- c = *++p;
- } else {
- *dst++ = '0';
- }
- }
- *dst++ = '.';
- if (c == '\0') {
- *dst++ = '0';
+ if (c != '\0') {
+ *dst++ = c;
+ c = *++p;
} else {
+ *dst++ = '0';
+ }
+ }
+ *dst++ = '.';
+ if (c == '\0') {
+ *dst++ = '0';
+ } else {
while (++exponent < -1) {
- *dst++ = '0';
- }
- while (c != '\0') {
- *dst++ = c;
- c = *++p;
- }
+ *dst++ = '0';
+ }
+ while (c != '\0') {
+ *dst++ = c;
+ c = *++p;
}
- *dst++ = '\0';
}
+ *dst++ = '\0';
+ }
ckfree(digits);
}