Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl Monk, Perl Meditation

Re^4: powerpc double-double arithmetic

by syphilis (Chancellor)
on Oct 10, 2013 at 03:44 UTC ( #1057671=note: print w/replies, xml ) Need Help??

in reply to Re^3: powerpc double-double arithmetic
in thread powerpc double-double arithmetic

for PPC, I guess sizeof is returning 16 for alignment reasons

With PPC, it actually uses the 16 bytes (in the form of 2 8-byte doubles).
There are other processors that use 12 bytes but assign 16 bytes (for alignment purposes, as you said).


Replies are listed 'Best First'.
Re^5: powerpc double-double arithmetic
by bulk88 (Priest) on Oct 10, 2013 at 12:00 UTC
    So if its vector math op (SSE, etc), its really 2 64 bit doubles and not a "long double". Long double would mean over 64 bits of double/precision. You have "packed data" not a "long double". Does your CPU have 128 bit FP math (see also) or not? Does your compiler emulate 128 bit FP math (GCC yes as __float128)?
      The basics of its arithmetic is here.
      There's no 128 bit FP math with its gcc-4.6.3 compiler. I think the double-double technique precludes it. (Every other gcc-4.6.3 that I've seen has a quadmath.h that provides the __float128 type, but not this one - which is provided by Debian specifically for the PowerPC architecture.)


Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://1057671]
and all is quiet...

How do I use this? | Other CB clients
Other Users?
Others having an uproarious good time at the Monastery: (3)
As of 2018-01-17 20:38 GMT
Find Nodes?
    Voting Booth?
    How did you see in the new year?

    Results (205 votes). Check out past polls.