Bell 32V development

[unix-history] / usr / src / libnm / tanh.s

# double tanh(arg)
# double arg
# method: tanh(arg)=sinh(arg)/cosh(arg); if |arg|<0.5 sinh(9 is computed from
# a polynomial approx otherwise from exp().
# Only 1 call to exp(9 is made.
# J F Jarvis, August 17, 1978
.globl _tanh
.globl _exp
.text
.align 1
_tanh:
       .word   0x7c0
       clrl    r10     # sign bit
       movd    4(ap),r6
       jgeq    t1
       movw    $0x8000,r10
       xorw2   r10,r6  # co|arg|
t1:     cmpd    r6,$0d2.0e+1
       jleq    t2
       movd    $0d1.0e+0,r0
       xorw2   r10,r0
       ret
t2:     movd    r6,-(sp)
       calls   $2,_exp
       movd    r0,r8
       divd3   r8,$0d1.0e+0,-(sp)      # exp(-|arg|)
       cmpd    r6,$0d0.5e+0
       jgeq    t3
       muld3   r6,r6,r0        # |arg|<0.5, sinh() from poly approx
       polyd   r0,$5,pcoef
       muld2   r6,r0
       muld2   $0d2.0e+0,r0    
       jbr     t4
t3:     subd3   (sp),r8,r0
t4:                             # r0,1 = 2*sinh(|arg|)
       addd3   (sp),r8,r2      # r2,3 = cosh(|arg|);
       divd2   r2,r0   # r0,1 = tanh(|arg|)
       xorw2   r10,r0  # r0,1 = tanh(arg)
       ret
.data
.align  3
pcoef:
       .double 0d0.251726188251e-7
       .double 0d0.275569807356154e-5
       .double 0d0.1984127027907999e-3
       .double 0d0.833333333307759961e-2
       .double 0d0.16666666666667212324e+0
       .double 0d0.99999999999999998116e+0