digitalmars.D - Size of the real type
- kinghajj (9/9) Mar 08 2006 This is just an FYI, but on my computer, this code:
- Jarrett Billingsley (4/6) Mar 08 2006 Odd! I get 80, as I'd expect.
- kinghajj (2/8) Mar 08 2006 DMD in Linux. I'll try runing it in Windows to see if that makes a difer...
- Unknown W. Brackets (4/18) Mar 08 2006 It does. As I recall, Walter has made past comments reflecting that the...
- =?ISO-8859-1?Q?Anders_F_Bj=F6rklund?= (15/26) Mar 08 2006 Side note:
- Jarrett Billingsley (7/20) Mar 09 2006 Which should be 80 on x86 processors!
- Walter Bright (10/15) Mar 09 2006 It's 96 bits on linux because gcc on linux pretends that 80 bit reals ar...
- Don Clugston (7/25) Mar 10 2006 The 128 bit convention makes some kind of sense -- it means an 80-bit
- Walter Bright (6/9) Mar 10 2006 It doesn't matter if it makes much sense or not, we're stuck with it on
This is just an FYI, but on my computer, this code:
import std.stdio;
int main(char[][] args)
{
writefln(real.sizeof * 8);
return 0;
}
Outputs the size of real as 96 bits, not 80.
I have an Intel Pentium 4 (Prescott) CPU.
Mar 08 2006
"kinghajj" <kinghajj_member pathlink.com> wrote in message news:duo1sh$1go1$1 digitaldaemon.com...This is just an FYI, but on my computer, this code: Outputs the size of real as 96 bits, not 80.Odd! I get 80, as I'd expect. Are you using DMD or GDC?
Mar 08 2006
In article <duoad7$1psv$1 digitaldaemon.com>, Jarrett Billingsley says..."kinghajj" <kinghajj_member pathlink.com> wrote in message news:duo1sh$1go1$1 digitaldaemon.com...DMD in Linux. I'll try runing it in Windows to see if that makes a diference.This is just an FYI, but on my computer, this code: Outputs the size of real as 96 bits, not 80.Odd! I get 80, as I'd expect. Are you using DMD or GDC?
Mar 08 2006
"Unknown W. Brackets" <unknown simplemachines.org> It does. As I recall, Walter has made past comments reflecting that the size of a real on Linux differs from the size of the same on Windows. I believe this is for library reasons. -[Unknown]In article <duoad7$1psv$1 digitaldaemon.com>, Jarrett Billingsley says..."kinghajj" <kinghajj_member pathlink.com> wrote in message news:duo1sh$1go1$1 digitaldaemon.com...DMD in Linux. I'll try runing it in Windows to see if that makes a diference.This is just an FYI, but on my computer, this code: Outputs the size of real as 96 bits, not 80.Odd! I get 80, as I'd expect. Are you using DMD or GDC?
Mar 08 2006
kinghajj wrote:This is just an FYI, but on my computer, this code: import std.stdio; int main(char[][] args) { writefln(real.sizeof * 8); return 0; }Side note: Who said the size of a "real" is 80 bits ? The size varies. It's just defined as: "largest hardware implemented FP size" I get 64, here on PowerPC :-) On a SPARC, you could get 128.Outputs the size of real as 96 bits, not 80. I have an Intel Pentium 4 (Prescott) CPU.The difference is due to alignment of the long double type. In x86 Linux, it is 96 bits. In x64 Linux, it is 128 bits... But they both still only use 80 bits, just add some padding. --anders PS. http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gcc/i386-and-x86_002d64-Options.html "The i386 application binary interface specifies the size to be 96 bits, so -m96bit-long-double is the default in 32 bit mode." [...] "In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI specifies that long double is to be aligned on 16 byte boundary."
Mar 08 2006
"Anders F Björklund" <afb algonet.se> wrote in message news:duol0f$278j$1 digitaldaemon.com...Side note: Who said the size of a "real" is 80 bits ? The size varies. It's just defined as: "largest hardware implemented FP size"Which should be 80 on x86 processors!The difference is due to alignment of the long double type. In x86 Linux, it is 96 bits. In x64 Linux, it is 128 bits... But they both still only use 80 bits, just add some padding. --anders PS. http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gcc/i386-and-x86_002d64-Options.html "The i386 application binary interface specifies the size to be 96 bits, so -m96bit-long-double is the default in 32 bit mode." [...] "In the x86-64 compiler, -m128bit-long-double is the default choice as its ABI specifies that long double is to be aligned on 16 byte boundary."Well if the only difference is in the alignment, why isn't just the real.alignof field affected? An x86-32 real is 80 bits, period. Or does it have to do with, say, C function name mangling? So a C function that takes one real in Windows would be _Name 80 but in Linux it'd be _Name 96 ?
Mar 09 2006
"Jarrett Billingsley" <kb3ctd2 yahoo.com> wrote in message news:dupgi5$g9f$2 digitaldaemon.com...Well if the only difference is in the alignment, why isn't just the real.alignof field affected? An x86-32 real is 80 bits, period. Or does it have to do with, say, C function name mangling? So a C function that takes one real in Windows would be _Name 80 but in Linux it'd be _Name 96 ?It's 96 bits on linux because gcc on linux pretends that 80 bit reals are really 96 bits long. What the alignment is is something different again. Name mangling does not drive this, although the "Windows" calling convention will have different names as you point out, but that doesn't matter. 96 bit convention permeates linux, and since D must be C ABI compatible with the host system's default C compiler, 96 bits it is on linux. If you're looking for mantissa significant bits, etc., use the various .properties of float types.
Mar 09 2006
Walter Bright wrote:"Jarrett Billingsley" <kb3ctd2 yahoo.com> wrote in message news:dupgi5$g9f$2 digitaldaemon.com...The 128 bit convention makes some kind of sense -- it means an 80-bit real is binary compatible with the proposed IEEE quad type (it just sets the last few mantissa bits to zero). But the 96 bit case makes no sense to me at all. pragma's DDL lets you (to some extent) mix Linux and Windows .objs. Eventually, we may need some way to deal with the different padding.Well if the only difference is in the alignment, why isn't just the real.alignof field affected? An x86-32 real is 80 bits, period. Or does it have to do with, say, C function name mangling? So a C function that takes one real in Windows would be _Name 80 but in Linux it'd be _Name 96 ?It's 96 bits on linux because gcc on linux pretends that 80 bit reals are really 96 bits long. What the alignment is is something different again. Name mangling does not drive this, although the "Windows" calling convention will have different names as you point out, but that doesn't matter. 96 bit convention permeates linux, and since D must be C ABI compatible with the host system's default C compiler, 96 bits it is on linux. If you're looking for mantissa significant bits, etc., use the various .properties of float types.
Mar 10 2006
"Don Clugston" <dac nospam.com.au> wrote in message news:durcq4$2u8o$1 digitaldaemon.com...But the 96 bit case makes no sense to me at all.It doesn't matter if it makes much sense or not, we're stuck with it on linux.pragma's DDL lets you (to some extent) mix Linux and Windows .objs. Eventually, we may need some way to deal with the different padding.I think it's a pipe dream to expect to be able to mix obj files between operating systems. The 96 bit thing is far from the only difference.
Mar 10 2006