C Floating point arithmetic

Ken Turkowski ken at turtlevax.UUCP
Fri Dec 6 06:31:47 AEST 1985

In article <7849 at ucla-cs.ARPA> jimc at ucla-cs.UUCP (Jim Carter) writes:
>    As for short-int-long conversions, I don't know of any machines where
>loading 16 bits into a 32-bit register is any slower than loading 32 bits.

However, if an int is a long, and your C compiler does all operations
on longs, then it takes at least one extra instruction to either sign-
or zero-extend a short or char to a long. So to add two shorts, you have:
	move16	_a,r0
	ext32	r0
	move16	_b,r1
	ext32	r1
	add32	r1,r0
	move16	r0,_a
Rather than
	move16	_a,r0
	add16	_b,r0
	move16	r0,_a
	add16	_b,_a
Can you say "order of magnitude in speed difference"?
Ken Turkowski @ CIMLINC, Menlo Park, CA
UUCP: {amd,decwrl,hplabs,seismo,spar}!turtlevax!ken
ARPA: turtlevax!ken at DECWRL.DEC.COM

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