[Bug gas/24944] New: gas doesn't read all necessary ditits when parse a floating point number

[jbgg.gnu at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=24944

            Bug ID: 24944
           Summary: gas doesn't read all necessary ditits when parse a
                    floating point number
           Product: binutils
           Version: 2.33 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: jbgg.gnu at gmail dot com
  Target Milestone: ---

Created attachment 11966
  --> https://sourceware.org/bugzilla/attachment.cgi?id=11966&action=edit
Patch for this bug

The pseudo instruction .double doesn't work fine parsing some numbers.
The function atof_generic doesn't read all digits of the number.

POC:
$ cat << EOF | as -o tmp && objdump -s tmp
.data
.double 37778931862957165903873.0
EOF

Output of previous command is:

tmp:     file format elf64-x86-64

Contents of section .data:
0000 00000000 0000a044                    .......D

We note that number N=37778931862957165903873.0 is calculated with bc with
command:

$echo 'e=75; 2^e + 2^(e-53) + 1' | bc

Then the numbers a=2^75 and b=(1+2^-52)*2^75 are the below and above
approximation of N to a double floating number. The output of previous
command shows that .double instruction chooses 2^75 as double aproximation,
although floating number (1+2^-52)*2^75 is closest to N since N=(a+b)/2 + 1.

This is due to a variable called ``maximum_useful_digits'' which limits the
number of read digits.

We can replace the variable ``maximum_useful_digits'' by the variable
``number_of_digits_available''.


gas/Changelog:
        * atof-generic.c: Delete the variable maximum_useful_digits.
        * testsuite/gas/i386/fp.s: add numbers where this bugs ocurrs.
        * testsuite/gas/i386/fp.d: correct output.

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