Article View: comp.arch
Article #12520Re: Swap byte instruction - how high is the win?
From: Piercarlo Grandi
Date: Sat, 09 Jan 1993 11:45
Date: Sat, 09 Jan 1993 11:45
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1993 bytes
On 8 Jan 93 04:35:25 GMT, prener@watson.ibm.com (Dan Prener) said: prener> (Volker Herminghaus-Shirai) writes: Volker> Subject line almost says it all. Many modern processors have an Volker> instruction to swap the bytes in a word. [ ... ] There must be Volker> *some* resaon why the RISC folks put it in, right? prener> The win is approximately zero for general code. But it is prener> significant for emulating a processor with the opposite byte prener> order. This is one reason: emulating a little endian x86 on a a big endian RISC machine. The other two reasons are: Dealing efficiently with data to/from a little endian OS (usually MSDOS or VMS) on a big endian machine. Dealing efficiently with network byte order (big endian) on a little endian machine. Summary: two extremely important architectures (x86 and VAX) are little endian; another two (68000, i.e. Mac and Sun) and network byte order are big endian; RISC machines tend to be big endian, but want to support interchange of data and emulation of little endian ones. Some RISC architectures are endian configurable for this reason. -- Piercarlo Grandi, Dept of CS, PC/UW@Aberystwyth <pcg@aber.ac.uk> E l'italiano cantava, cantava. E le sue disperate invocazioni giunsero alle orecchie del suo divino protettore, il dio della barzelletta
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Path: arc1-ca.pugleaf.net!sparky!uunet!spool.mu.edu!agate!doc.ic.ac.uk!uknet!gdt!aber!fronta.aber.ac.uk!pcg From: pcg@aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.arch Subject: Re: Swap byte instruction - how high is the win? Message-ID: <PCG.93Jan9114543@decb.aber.ac.uk> Date: 9 Jan 93 11:45:43 GMT References: <1993Jan7.074052.19620@qb.rhein-main.de> <PRENER.93Jan7233525@prener.watson.ibm.com> Sender: news@aber.ac.uk (USENET news service) Reply-To: pcg@aber.ac.uk (Piercarlo Grandi) Organization: Prifysgol Cymru, Aberystwyth Lines: 31 In-Reply-To: prener@watson.ibm.com's message of 8 Jan 93 04: 35:25 GMT Nntp-Posting-Host: decb.aber.ac.uk