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changeset 23556:31b1ef1ee585

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Fix Octave's -text format for saving data to make it lossless for IEEE-754 doubles. * ls-oct-text.cc (Vsave_precision): Change default to 17 digits. * ls-oct-text.cc (Fsave_precision): Add explanation of suitable values to docstring.
author Rik <rik@octave.org>
date Wed, 07 Jun 2017 12:29:23 -0700
parents 9151922777e2
children 00b11cee2100
files libinterp/corefcn/ls-oct-text.cc
diffstat 1 files changed, 11 insertions(+), 2 deletions(-) [+]
line wrap: on
line diff
--- a/libinterp/corefcn/ls-oct-text.cc	Wed Jun 07 12:11:33 2017 -0700
+++ b/libinterp/corefcn/ls-oct-text.cc	Wed Jun 07 12:29:23 2017 -0700
@@ -64,8 +64,9 @@
 #include "version.h"
 #include "dMatrix.h"
 
-// The number of decimal digits to use when writing ascii data.
-static int Vsave_precision = 16;
+// The number of decimal digits to use when writing ASCII data.
+// 17 is the minimum necessary for lossless save/restore of IEEE-754 doubles.
+static int Vsave_precision = 17;
 
 // Functions for reading octave format text data.
 
@@ -406,9 +407,17 @@
 Query or set the internal variable that specifies the number of digits to
 keep when saving data in text format.
 
+The default value is 17 which is the minimum necessary for the lossless saving
+and restoring of IEEE-754 double values; For IEEE-754 single values the minimum
+value is 9.  If file size is a concern, it is probably better to choose a
+binary format for saving data rather than to reduce the precision of the saved
+values.
+
 When called from inside a function with the @qcode{"local"} option, the
 variable is changed locally for the function and any subroutines it calls.
 The original variable value is restored when exiting the function.
+
+@seealso{save_default_options}
 @end deftypefn */)
 {
   return SET_INTERNAL_VARIABLE_WITH_LIMITS (save_precision, -1,