linux-kernel - Re: Using __int128 on 64-bit architectures

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Message-Id: <20130421193531.43965f592f00dfd6e3cfcf45@canb.auug.org.au>
Date:	Sun, 21 Apr 2013 19:35:31 +1000
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linux Arch Mailing List <linux-arch@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Using __int128 on 64-bit architectures

On Sun, 21 Apr 2013 05:29:28 +0100 (BST) "Maciej W. Rozycki" <macro@...ux-mips.org> wrote:
>
>  Hmm, nobody has replied, so just FYI such widening multiplication is 
> available in all 64-bit MIPS hardware and GCC has supported it since 4.4 
> or mid 2008 (older versions used a libgcc __multi3 helper, not quite so 
> efficient as you can imagine).

$ powerpc64-linux-gcc --version
powerpc64-linux-gcc (GCC) 4.6.3
  ...
$ powerpc64-linux-gcc -O2 -c mulditi3.c
$ powerpc64-linux-objdump -d -r mulditi3.o
mulditi3.o:     file format elf64-powerpc

Disassembly of section .text:

0000000000000000 <.mulditi3>:
   0:	7c 08 02 a6 	mflr    r0
   4:	7c 86 23 78 	mr      r6,r4
   8:	7c c5 fe 76 	sradi   r5,r6,63
   c:	f8 01 00 10 	std     r0,16(r1)
  10:	7c 64 1b 78 	mr      r4,r3
  14:	f8 21 ff 91 	stdu    r1,-112(r1)
  18:	7c 63 fe 76 	sradi   r3,r3,63
  1c:	48 00 00 01 	bl      1c <.mulditi3+0x1c>
			1c: R_PPC64_REL24	__multi3
  20:	60 00 00 00 	nop
  24:	38 21 00 70 	addi    r1,r1,112
  28:	e8 01 00 10 	ld      r0,16(r1)
  2c:	7c 08 03 a6 	mtlr    r0
  30:	4e 80 00 20 	blr
  34:	00 00 00 00 	.long 0x0
  38:	00 00 00 01 	.long 0x1
  3c:	80 00 00 00 	lwz     r0,0(0)
$ 

i.e. for gcc 4.6.3, 64 bit powerpc calls out to __multi3

The same is true for sparc64.

-- 
Cheers,
Stephen Rothwell                    sfr@...b.auug.org.au

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