usr/src/lib/libm/tahoe/cabs.s

#
# Copyright (c) 1987 Regents of the University of California.
# All rights reserved.
#
# Redistribution and use in source and binary forms are permitted
# provided that this notice is preserved and that due credit is given
# to the University of California at Berkeley. The name of the University
# may not be used to endorse or promote products derived from this
# software without specific prior written permission. This software
# is provided ``as is'' without express or implied warranty.
#
# All recipients should regard themselves as participants in an ongoing
# research project and hence should feel obligated to report their
# experiences (good or bad) with these elementary function codes, using
# the sendbug(8) program, to the authors.
#
#       @(#)cabs.s      5.3 (Berkeley) %G%
#
        .data
        .align  2
_sccsid:
.asciz  "@(#)cabs.s     5.3     5.3     (ucb.elefunt)   %G%"

# 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(fp)
# argument for cabs and hypot (C fcns) by value, 4(fp)
# output is in r0:r1

        .text
        .align  2
        .globl  _cabs
        .globl  _hypot
        .globl  _z_abs

#       entry for c functions cabs and hypot
_cabs:
_hypot:
        .word   0x807c          # save r2-r6, enable floating overflow
        movl    16(fp),r3
        movl    12(fp),r2       # r2:3 = y
        movl    8(fp),r1
        movl    4(fp),r0        # r0:1 = x
        brb     1f
#       entry for Fortran use, call by:   d = abs(z)
_z_abs:
        .word   0x807c          # save r2-r6, enable floating overflow
        movl    4(fp),r4        # indirect addressing is necessary here
        movl    12(r4),r3       #
        movl    8(r4),r2        # r2:3 = y
        movl    4(r4),r1        #
        movl    (r4),r0         # r0:1 = x
1:      andl3   $0xff800000,r0,r4       # r4 has signed biased exp of x
        cmpl    $0x80000000,r4
        beql    2f              # x is a reserved operand, so return it
        andl3   $0xff800000,r2,r5       # r5 has signed biased exp of y
        cmpl    $0x80000000,r5
        bneq    3f              # y isn't a reserved operand
        movl    r3,r1
        movl    r2,r0           # return y if it's reserved
2:      ret

3:      callf   $4,regs_set     # r0:1 = dsqrt(x^2+y^2)/2^r6
        addl2   r6,r0           # unscaled cdabs in r0:1
        jvc     2b              # unless it overflows
        subl2   $0x800000,r0    # halve r0 to get meaningful overflow
        ldd     r0
        addd    r0              # overflow; r0 is half of true abs value
        ret

regs_set:
        .word   0x0000
        andl2   $0x7fffffff,r0  # r0:r1 = dabs(x)
        andl2   $0x7fffffff,r2  # r2:r3 = dabs(y)
        cmpl    r0,r2
        bgeq    4f
        movl    r1,r5
        movl    r0,r4
        movl    r3,r1
        movl    r2,r0
        movl    r5,r3
        movl    r4,r2           # force y's exp <= x's exp
4:      andl3   $0xff800000,r0,r6       # r6 = exponent(x) + bias(129)
        beql    5f              # if x = y = 0 then cdabs(x,y) = 0
        subl2   $0x47800000,r6  # r6 = exponent(x) - 14
        subl2   r6,r0           # 2^14 <= scaled x < 2^15
        bitl    $0xff800000,r2
        beql    5f              # if y = 0 return dabs(x)
        subl2   r6,r2
        cmpl    $0x37800000,r2  # if scaled y < 2^-18
        bgtr    5f              #   return dabs(x)
        ldd     r0
        muld    r0
        std     r0              # r0:1 = scaled x^2
        ldd     r2
        muld    r2              # acc = scaled y^2
        addd    r0
        std     r0
        pushl   r1
        pushl   r0
        callf   $12,_sqrt       # r0:1 = dsqrt(x^2+y^2)/2^r6
5:      ret