Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!leah!rpi!batcomputer!cornell!uw-beaver!uw-entropy!dataio!bright
From: bright@Data-IO.COM (Walter Bright)
Newsgroups: comp.lang.c
Subject: Re: iAPX86 code for ABS (using Microsoft C?)
Message-ID: <2083@dataio.Data-IO.COM>
Date: 2 Aug 89 18:05:06 GMT
References: <1202@draken.nada.kth.se>
Reply-To: bright@dataio.Data-IO.COM (Walter Bright)
Organization: Data I/O Corporation; Redmond, WA
Lines: 22

In article <1202@draken.nada.kth.se> d88-eli@nada.kth.se (Erik Liljencrantz) writes:
>The function to convert an integer
>to a positive integer was performed without a conditional jump (i.e. JS or
>something). I'm very interested in this piece of code,

This is a well-known trick:

;;;;;;;;;;;;;;;;;;;;;;;;;
; Take absolute value of integer.

	c_public abs

func	abs
	push	BP
	mov	BP,SP
	mov	AX,P[BP]
	cwd
	xor	AX,DX		;look, ma, no jumps!
	sub	AX,DX
	pop	BP
	ret
c_endp	abs