Can GDB correctly parse C-style hexadecimal floating-point numbers?

Question

I cannot manage to make GDB print correctly some C-style hexadecimal floating-point numbers, see:

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(gdb) p 0xa.0p-4
$1 = 6

Here $1 should be 0.625 but my GDB seems to see 0xa.0p as decimal 10 and does a subsequent addition with -4. What is wrong with what I ask GDB to print? I could not find any relevant documentation on how GDB handles hexadecimal floats.

Answer 1

What is wrong with what I ask GDB to print?

Apparently it's a bug with gdb.

Hexadecimal floating point constants with a negative exponent give a wrong result with gdb.

I tried with the latest source release gdb 7.9 (Feb 20, 2015) on Linux and hexadecimal floating point constants with a positive exponent are supported:

(gdb) p/f 0x00.1p0
$1 = 0.0625
(gdb) p/f 0x00.1p1
$2 = 0.125

but if the exponent is negative, then the result is wrong:

(gdb) p/f 0x00.1p-1
$3 = -0.9375

The right and expected result is 0.031250.