diff options
Diffstat (limited to 'doc/tclvars.n')
| -rw-r--r-- | doc/tclvars.n | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/doc/tclvars.n b/doc/tclvars.n index 6ffb6a0..627fb6f 100644 --- a/doc/tclvars.n +++ b/doc/tclvars.n @@ -5,7 +5,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: tclvars.n,v 1.21 2005/04/06 20:55:24 dkf Exp $ +'\" RCS: @(#) $Id: tclvars.n,v 1.22 2005/05/10 18:34:03 kennykb Exp $ '\" .so man.macros .TH tclvars n 8.0 Tcl "Tcl Built-In Commands" @@ -242,7 +242,20 @@ is same as the result of evaluating \fIsizeof(long)\fR in C.) \fBtcl_precision\fR This variable controls the number of digits to generate when converting floating-point values to strings. It defaults -to 12. +.VS 8.5 +to 0. \fIApplications should not change this value;\fR it is +provided for compatibility with legacy code. +.PP +The default value of 0 is special, meaning that Tcl should +convert numbers using as few digits as possible while still +distinguishing any floating point number from its nearest +neighbours. It differs from using an arbitrarily high value +for \fItcl_precision\fR in that an inexact number like \fI1.4\fR +will convert as \fI1.4\fR rather than \fI1.3999999999999999\fR +even though the latter is nearer to the exact value of the +binary number. +.VE 8.5 +.PP 17 digits is ``perfect'' for IEEE floating-point in that it allows double-precision values to be converted to strings and back to binary with no loss of information. However, using 17 digits prevents |