diff options
Diffstat (limited to 'generic/tclUtil.c')
| -rw-r--r-- | generic/tclUtil.c | 54 |
1 files changed, 51 insertions, 3 deletions
diff --git a/generic/tclUtil.c b/generic/tclUtil.c index 984ba0a..f746aed 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 1.123 2010/12/03 22:30:56 hobbs Exp $ + * RCS: @(#) $Id: tclUtil.c,v 1.124 2011/01/15 18:10:19 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) { @@ -2294,7 +2334,15 @@ Tcl_PrintDouble( 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 { + sprintf(dst, "e%+03d", exponent); + } } else { /* * F format for others. |