Re^2: Large floating point literals

Thanks!! I had, foolishly, not considered that the displayed base 10 might be rounded.

Several literals slightly larger than 1.797693134862314e+308 are converted to non-infinite numbers, including two in the following test that are converted to what I believe is the largest possible value.

use strict;
use warnings;
use Devel::Peek;

foreach my $x (
    [ '1.797693134862314e+308' , 1.797693134862314e+308 ],
    [ '1.7976931348623141e+308' , 1.7976931348623141e+308 ],
    [ '1.7976931348623142e+308' , 1.7976931348623142e+308 ],
    [ '1.7976931348623143e+308' , 1.7976931348623143e+308 ],
    [ '1.7976931348623144e+308' , 1.7976931348623144e+308 ],
    [ '1.7976931348623145e+308' , 1.7976931348623145e+308 ],
    [ '1.7976931348623146e+308' , 1.7976931348623146e+308 ],
    [ '1.7976931348623147e+308' , 1.7976931348623147e+308 ],
    [ '1.7976931348623148e+308' , 1.7976931348623148e+308 ],
    [ '1.7976931348623149e+308' , 1.7976931348623149e+308 ],
    [ '1.7976931348623150e+308' , 1.7976931348623150e+308 ],
    [ '1.7976931348623151e+308' , 1.7976931348623151e+308 ],
    [ '1.7976931348623152e+308' , 1.7976931348623152e+308 ],
    [ '1.7976931348623153e+308' , 1.7976931348623153e+308 ],
    [ '1.7976931348623154e+308' , 1.7976931348623154e+308 ],
    [ '1.7976931348623155e+308' , 1.7976931348623155e+308 ],
    [ '1.7976931348623156e+308' , 1.7976931348623156e+308 ],
    [ '1.7976931348623157e+308' , 1.7976931348623157e+308 ],
    [ '1.7976931348623158e+308' , 1.7976931348623158e+308 ],
    [ '1.7976931348623159e+308' , 1.7976931348623159e+308 ],
) {
    my ($string, $number) = @$x;

    print "$string\n";
    Dump($number);

    my $foo = pack('d', $number);
    Dump($foo);
    print "\n";
}

__END__

1.797693134862314e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\366\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623141e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\367\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623142e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\367\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623143e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\370\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623144e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\370\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623145e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\371\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623146e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\372\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623147e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\372\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623148e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\373\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623149e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486231e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\373\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623150e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\374\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623151e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\374\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623152e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\375\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623153e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\375\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623154e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\376\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623155e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\376\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623156e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\377\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623157e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = 1.79769313486232e+308
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\377\377\377\377\377\377\357\177"\0
  CUR = 8
  LEN = 12

1.7976931348623158e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = inf
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\0\0\0\0\0\0\360\177"\0
  CUR = 8
  LEN = 12

1.7976931348623159e+308
SV = NV(0x88c58c8) at 0x88f0b50
  REFCNT = 1
  FLAGS = (PADMY,NOK,pNOK)
  NV = inf
SV = PV(0x88ed958) at 0x88f0bc0
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x88a7308 "\0\0\0\0\0\0\360\177"\0
  CUR = 8
  LEN = 12
[download]

Comment on Re^2: Large floating point literals Download Code

Replies are listed 'Best First'.
Re^3: Large floating point literals by BrowserUk (Patriarch) on May 20, 2009 at 23:22 UTC
Indeed. You are correct. I chose the wrong reference: `printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0x7fefffff, 0x +ffffffff;; 1.7976931348623157e+308 printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0x7fffffff, 0x +ffffffff;; 1.#QNAN printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0xffefffff, 0x +ffffffff;; -1.7976931348623157e+308 printf "%.20g\n", unpack 'd', scalar reverse pack 'NN', 0xffffffff, 0x +ffffffff;; -1.#QNAN` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]
Re^4: Large floating point literals by ig (Vicar) on May 21, 2009 at 00:53 UTC
I never tried it before but Math::BigInt can be used to see these numbers in full precision. Read more... (4 kB)	[reply] [d/l]
Re^5: Large floating point literals by BrowserUk (Patriarch) on May 21, 2009 at 01:21 UTC
It's cool if you need the precision and can live with the performance of infinite precision--which is generally abysmal. But don't forget that on modern x86 and x64 hardware, the FPU uses 80-bit floats internally even when the calling code is using 64-bit floats. That greatly reduces the loss of precision of intermediate calculations provided that the math libraries are well written. Ie. They don't move intermediate values out of the FPU to ram and back again. How effective Perl's math routines are at keeping intermediate values in the FPU registers I have no idea. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]