Longjmping back, and back again; Coroutines in C

[Kenneth L Moore]

In article <1989Nov21.120938.9200 at psuvax1.cs.psu.edu> flee at shire.cs.psu.edu (Felix Lee) writes:
==>Jerker W}gberg <jerker at helios.se==> wrote:
==>==> The idea is that instead of actually switching stacks, I use the
==>==> "real" stack but swap it in and out of malloced memory.
==>==> 1. Can somebody explain why this fails on a SUN4.
==>
==>The Sun-4 has a curious hack known as register windows.  Rather than
==>putting things on the stack, it keeps everything in registers.  Each
==>subroutine gets its own set of 24 registers called a register window.
==>For passing arguments, register windows overlap: 8 output registers in
==>your window become input registers when you call another subroutine.
==>
==>--
==>Felix Lee	flee at shire.cs.psu.edu	*!psuvax1!flee

Yup. This is state of the art computater (sic) architecture. This idea
arose along with RISC (Reduced Instruction Set Computer) but can be used
on RISC or CISC (Complex Instruction Set Computer) machines.

Remember that RISC is the result of a statistical study that showed that
99% of the instructions used on a CISC machine were a sub-set of some 30
(out of maybe 256? on an IBM 360) commands. Also, 10 instructions
accounted for 80% and 21 accounted for 95%.

Another aspect that became apparent during these studies was that much
of the overhead in a processor was consumed in keeping track of
subroutine calls and returns.

The original RISC-I guys had a lot of left over chip area and decided
that the thing to do with the extra area was to make extra registers.
And they shrewdly decided to use the registers to facilitate subroutine
handling.

C programmers, keep these facts in mind as they will dominate computer
architecture in the near term.

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kenmoore at unix.cis.pitt.edu (Kenneth L. Moore)

(Sorry about the long signature but inews won't recognise my .signature...
even after "chmod 777 .signature". Tsk. Tsk.)