xref: /src/lib/libm/arch/vax/n_cabs.S

/*	$NetBSD: n_cabs.S,v 1.8 2024/05/07 15:15:09 riastradh Exp $	*/
/*
 * Copyright (c) 1985, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)cabs.s	8.1 (Berkeley) 6/4/93
 */

#include <machine/asm.h>

	.globl	_C_LABEL(__libm_dsqrt_r5)
/*
 * double precision complex absolute value
 * CABS by W. Kahan, 9/7/80.
 * Revised for reserved operands by E. LeBlanc, 8/18/82
 * argument for complex absolute value by reference, *4(%ap)
 * argument for cabs and hypot (C fcns) by value, 4(%ap)
 * output is in %r0:%r1 (error less than 0.86 ulps)
 */

/*	entry for c functions cabs and hypot */
#ifdef WEAK_ALIAS
WEAK_ALIAS(hypotf, _hypotf)
#endif

ENTRY(_hypotf, 0)
	cvtfd	4(%ap),-(%sp)
	calls	$2,_C_LABEL(_hypot)
	cvtdf	%r0,%r0
	ret
END(_hypotf)

#ifdef WEAK_ALIAS
WEAK_ALIAS(hypot, _hypot)
WEAK_ALIAS(hypotl, _hypot)
WEAK_ALIAS(_hypotl, _hypot)
#endif

ALTENTRY(cabs)
ENTRY(_hypot, 0x8040) 		# save %r6, enable floating overflow
	movq	4(%ap),%r0	# %r0:1 = x
	movq	12(%ap),%r2	# %r2:3 = y
	jbr	cabs2
END(_hypot)

/*	entry for Fortran use, call by:   d = abs(z) */
ENTRY(z_abs, 0x8040)		# save %r6, enable floating overflow
	movl	4(%ap),%r2	# indirect addressing is necessary here
	movq	(%r2)+,%r0	# %r0:1 = x
	movq	(%r2),%r2		# %r2:3 = y

cabs2:
	bicw3	$0x7f,%r0,%r4	# %r4 has signed biased exp of x
	cmpw	$0x8000,%r4
	jeql	return		# x is a reserved operand, so return it
	bicw3	$0x7f,%r2,%r5	# %r5 has signed biased exp of y
	cmpw	$0x8000,%r5
	jneq	cont		/* y isn't a reserved operand */
	movq	%r2,%r0		/* return y if it's reserved */
	ret

cont:
	bsbb	regs_set	# %r0:1 = dsqrt(x^2+y^2)/2^%r6
	addw2	%r6,%r0		# unscaled cdabs in %r0:1
	jvc	return		# unless it overflows
	subw2	$0x80,%r0	# halve %r0 to get meaningful overflow
	addd2	%r0,%r0		# overflow; %r0 is half of true abs value
return:
	ret
END(z_abs)

ENTRY(__libm_cdabs_r6,0)	# ENTRY POINT for cdsqrt
				# calculates a scaled (factor in %r6)
				# complex absolute value

	movq	(%r4)+,%r0	# %r0:%r1 = x via indirect addressing
	movq	(%r4),%r2		# %r2:%r3 = y via indirect addressing

	bicw3	$0x7f,%r0,%r5	# %r5 has signed biased exp of x
	cmpw	$0x8000,%r5
	jeql	cdreserved	# x is a reserved operand
	bicw3	$0x7f,%r2,%r5	# %r5 has signed biased exp of y
	cmpw	$0x8000,%r5
	jneq	regs_set	/* y isn't a reserved operand either? */

cdreserved:
	movl	*4(%ap),%r4	# %r4 -> (u,v), if x or y is reserved
	movq	%r0,(%r4)+	# copy u and v as is and return
	movq	%r2,(%r4)		# (again addressing is indirect)
	ret

regs_set:
	bicw2	$0x8000,%r0	# %r0:%r1 = dabs(x)
	bicw2	$0x8000,%r2	# %r2:%r3 = dabs(y)
	cmpw	%r0,%r2
	jgeq	ordered
	movq	%r0,%r4
	movq	%r2,%r0
	movq	%r4,%r2		# force y's exp <= x's exp
ordered:
	bicw3	$0x7f,%r0,%r6	# %r6 = exponent(x) + bias(129)
	jeql	retsb		# if x = y = 0 then cdabs(x,y) = 0
	subw2	$0x4780,%r6	# %r6 = exponent(x) - 14
	subw2	%r6,%r0		# 2^14 <= scaled x < 2^15
	bitw	$0xff80,%r2
	jeql	retsb		# if y = 0 return dabs(x)
	subw2	%r6,%r2
	cmpw	$0x3780,%r2	# if scaled y < 2^-18
	jgtr	retsb		#   return dabs(x)
	emodd	%r0,$0,%r0,%r4,%r0	# %r4 + %r0:1 = scaled x^2
	emodd	%r2,$0,%r2,%r5,%r2	# %r5 + %r2:3 = scaled y^2
	addd2	%r2,%r0
	addl2	%r5,%r4
	cvtld	%r4,%r2
	addd2	%r2,%r0		# %r0:1 = scaled x^2 + y^2
	jmp	_C_LABEL(__libm_dsqrt_r5)+2
				# %r0:1 = dsqrt(x^2+y^2)/2^%r6
retsb:
	rsb			# error < 0.86 ulp
END(__libm_cdabs_r6)