Harkening back to my experiments to make an Expand.pm to interpret IEEE754 doubles, I found when making my tests that as I converted a signaling NaN bit string into a double then back to the bit string, it became a quiet NaN. At first I thought I just had a bug in my conversion, so then I tried BrowserUK's code from Re^2: Exploring IEEE754 floating point bit patterns., along with a new function to convert it back.

#!/usr/bin/perl

use warnings;
use strict;
use lib '.';
use Tools;  # local == Data::IEEE754::Tools

use constant {
    POS_ZERO        => '0'.'00000000000'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    POS_DENORM_1ST  => '0'.'00000000000'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000001',
    POS_DENORM_LST  => '0'.'00000000000'.'1111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    POS_NORM_1ST    => '0'.'00000000001'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    POS_NORM_LST    => '0'.'11111111110'.'1111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    POS_INF         => '0'.'11111111111'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    POS_SNAN_1ST    => '0'.'11111111111'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000001',
    POS_SNAN_LST    => '0'.'11111111111'.'0111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    POS_IND         => '0'.'11111111111'.'1000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    POS_QNAN_1ST    => '0'.'11111111111'.'1000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000001',
    POS_QNAN_LST    => '0'.'11111111111'.'1111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    NEG_ZERO        => '1'.'00000000000'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    NEG_DENORM_1ST  => '1'.'00000000000'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000001',
    NEG_DENORM_LST  => '1'.'00000000000'.'1111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    NEG_NORM_1ST    => '1'.'00000000001'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    NEG_NORM_LST    => '1'.'11111111110'.'1111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    NEG_INF         => '1'.'11111111111'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    NEG_SNAN_1ST    => '1'.'11111111111'.'0000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000001',
    NEG_SNAN_LST    => '1'.'11111111111'.'0111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',
    NEG_IND         => '1'.'11111111111'.'1000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000000',
    NEG_QNAN_1ST    => '1'.'11111111111'.'1000'.'00000000'.'00000000'.
+'00000000'.'00000000'.'00000000'.'00000001',
    NEG_QNAN_LST    => '1'.'11111111111'.'1111'.'11111111'.'11111111'.
+'11111111'.'11111111'.'11111111'.'11111111',  
};
my @list = (
    POS_ZERO, POS_DENORM_1ST, POS_DENORM_LST, POS_NORM_1ST, POS_NORM_L
+ST,
    POS_INF, POS_SNAN_1ST, POS_SNAN_LST,
    POS_IND, POS_QNAN_1ST, POS_QNAN_LST,
    NEG_ZERO, NEG_DENORM_1ST, NEG_DENORM_LST, NEG_NORM_1ST, NEG_NORM_L
+ST,
    NEG_INF, NEG_SNAN_1ST, NEG_SNAN_LST,
    NEG_IND, NEG_QNAN_1ST, NEG_QNAN_LST
);

sub bitsToDouble{ unpack 'd',  pack 'b64', scalar reverse $_[0] }
sub bitsToInts{   reverse unpack 'VV', pack 'b64', scalar reverse $_[0
+] }
sub doubleToBits{ scalar reverse unpack 'b64', pack 'd', $_[0] }
printf "%23.16g : %08x%08x >=there-and-back-again=> %08x%08x\n", 
    bitsToDouble( $_ ), bitsToInts( $_ ), 
    bitsToInts( doubleToBits( bitsToDouble( $_ ) ) )
    for @list;

print "\n";

use Test::More tests => 22;
is( doubleToBits( bitsToDouble( $_ ) ) , $_ , "bitsToDouble(doubleToBi
+ts($_))" ) for @list;

[download]

outputs

                      0 : 0000000000000000 >=there-and-back-again=> 00
+00000000000000
 4.940656458412465e-324 : 0000000000000001 >=there-and-back-again=> 00
+00000000000001
 2.225073858507201e-308 : 000fffffffffffff >=there-and-back-again=> 00
+0fffffffffffff
 2.225073858507201e-308 : 0010000000000000 >=there-and-back-again=> 00
+10000000000000
 1.797693134862316e+308 : 7fefffffffffffff >=there-and-back-again=> 7f
+efffffffffffff
                    Inf : 7ff0000000000000 >=there-and-back-again=> 7f
+f0000000000000
                    NaN : 7ff0000000000001 >=there-and-back-again=> 7f
+f8000000000001
                    NaN : 7ff7ffffffffffff >=there-and-back-again=> 7f
+ffffffffffffff
                    NaN : 7ff8000000000000 >=there-and-back-again=> 7f
+f8000000000000
                    NaN : 7ff8000000000001 >=there-and-back-again=> 7f
+f8000000000001
                    NaN : 7fffffffffffffff >=there-and-back-again=> 7f
+ffffffffffffff
                     -0 : 8000000000000000 >=there-and-back-again=> 80
+00000000000000
-4.940656458412465e-324 : 8000000000000001 >=there-and-back-again=> 80
+00000000000001
-2.225073858507201e-308 : 800fffffffffffff >=there-and-back-again=> 80
+0fffffffffffff
-2.225073858507201e-308 : 8010000000000000 >=there-and-back-again=> 80
+10000000000000
-1.797693134862316e+308 : ffefffffffffffff >=there-and-back-again=> ff
+efffffffffffff
                   -Inf : fff0000000000000 >=there-and-back-again=> ff
+f0000000000000
                    NaN : fff0000000000001 >=there-and-back-again=> ff
+f8000000000001
                    NaN : fff7ffffffffffff >=there-and-back-again=> ff
+ffffffffffffff
                    NaN : fff8000000000000 >=there-and-back-again=> ff
+f8000000000000
                    NaN : fff8000000000001 >=there-and-back-again=> ff
+f8000000000001
                    NaN : ffffffffffffffff >=there-and-back-again=> ff
+ffffffffffffff

...
not ok 7 - bitsToDouble(doubleToBits(011111111111000000000000000000000
+0000000000000000000000000000001))
#   Failed test 'bitsToDouble(doubleToBits(011111111111000000000000000
+0000000000000000000000000000000000001))'
#   at ...\buk.pl line 52.
#          got: '01111111111110000000000000000000000000000000000000000
+00000000001'
#     expected: '01111111111100000000000000000000000000000000000000000
+00000000001'
not ok 8 - bitsToDouble(doubleToBits(011111111111011111111111111111111
+1111111111111111111111111111111))
#   Failed test 'bitsToDouble(doubleToBits(011111111111011111111111111
+1111111111111111111111111111111111111))'
#   at ...\buk.pl line 52.
#          got: '01111111111111111111111111111111111111111111111111111
+11111111111'
#     expected: '01111111111101111111111111111111111111111111111111111
+11111111111'
...
not ok 18 - bitsToDouble(doubleToBits(11111111111100000000000000000000
+00000000000000000000000000000001))
#   Failed test 'bitsToDouble(doubleToBits(111111111111000000000000000
+0000000000000000000000000000000000001))'
#   at ...\buk.pl line 52.
#          got: '11111111111110000000000000000000000000000000000000000
+00000000001'
#     expected: '11111111111100000000000000000000000000000000000000000
+00000000001'
not ok 19 - bitsToDouble(doubleToBits(11111111111101111111111111111111
+11111111111111111111111111111111))
#   Failed test 'bitsToDouble(doubleToBits(111111111111011111111111111
+1111111111111111111111111111111111111))'
#   at ...\buk.pl line 52.
#          got: '11111111111111111111111111111111111111111111111111111
+11111111111'
#     expected: '11111111111101111111111111111111111111111111111111111
+11111111111'
...

[download]

... ie, it fails on just the signaling NaN, appearing like a quiet NaN bitstring.

I tried under an ancient CentOS 4.6 perl 5.8.5, and under a recent Strawberry 5.22.1 32bit, and get the same quieting of the sNaN. Am I doing something wrong, or does perl just automatically quiet signalling NaN values?

In reply to unintentional conversion of signaling NaN to quiet NaN by pryrt

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