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|
|
| scale.sa 3.3 7/30/91
|
| The entry point sSCALE computes the destination operand
| scaled by the source operand. If the absolute value of
| the source operand is (>= 2^14) an overflow or underflow
| is returned.
|
| The entry point sscale is called from do_func to emulate
| the fscale unimplemented instruction.
|
| Input: Double-extended destination operand in FPTEMP,
| double-extended source operand in ETEMP.
|
| Output: The function returns scale(X,Y) to fp0.
|
| Modifies: fp0.
|
| Algorithm:
|
| Copyright (C) Motorola, Inc. 1990
| All Rights Reserved
|
| For details on the license for this file, please see the
| file, README, in this same directory.
|SCALE idnt 2,1 | Motorola 040 Floating Point Software Package
|section 8
#include "fpsp.h"
|xref t_ovfl2
|xref t_unfl
|xref round
|xref t_resdnrm
SRC_BNDS: .short 0x3fff,0x400c
|
| This entry point is used by the unimplemented instruction exception
| handler.
|
|
|
| FSCALE
|
.global sscale
sscale:
fmovel #0,%fpcr |clr user enabled exc
clrl %d1
movew FPTEMP(%a6),%d1 |get dest exponent
smi L_SCR1(%a6) |use L_SCR1 to hold sign
andil #0x7fff,%d1 |strip sign
movew ETEMP(%a6),%d0 |check src bounds
andiw #0x7fff,%d0 |clr sign bit
cmp2w SRC_BNDS,%d0
bccs src_in
cmpiw #0x400c,%d0 |test for too large
bge src_out
|
| The source input is below 1, so we check for denormalized numbers
| and set unfl.
|
src_small:
moveb DTAG(%a6),%d0
andib #0xe0,%d0
tstb %d0
beqs no_denorm
st STORE_FLG(%a6) |dest already contains result
orl #unfl_mask,USER_FPSR(%a6) |set UNFL
den_done:
leal FPTEMP(%a6),%a0
bra t_resdnrm
no_denorm:
fmovel USER_FPCR(%a6),%FPCR
fmovex FPTEMP(%a6),%fp0 |simply return dest
rts
|
| Source is within 2^14 range. To perform the int operation,
| move it to d0.
|
src_in:
fmovex ETEMP(%a6),%fp0 |move in src for int
fmovel #rz_mode,%fpcr |force rz for src conversion
fmovel %fp0,%d0 |int src to d0
fmovel #0,%FPSR |clr status from above
tstw ETEMP(%a6) |check src sign
blt src_neg
|
| Source is positive. Add the src to the dest exponent.
| The result can be denormalized, if src = 0, or overflow,
| if the result of the add sets a bit in the upper word.
|
src_pos:
tstw %d1 |check for denorm
beq dst_dnrm
addl %d0,%d1 |add src to dest exp
beqs denorm |if zero, result is denorm
cmpil #0x7fff,%d1 |test for overflow
bges ovfl
tstb L_SCR1(%a6)
beqs spos_pos
orw #0x8000,%d1
spos_pos:
movew %d1,FPTEMP(%a6) |result in FPTEMP
fmovel USER_FPCR(%a6),%FPCR
fmovex FPTEMP(%a6),%fp0 |write result to fp0
rts
ovfl:
tstb L_SCR1(%a6)
beqs sovl_pos
orw #0x8000,%d1
sovl_pos:
movew FPTEMP(%a6),ETEMP(%a6) |result in ETEMP
movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
bra t_ovfl2
denorm:
tstb L_SCR1(%a6)
beqs den_pos
orw #0x8000,%d1
den_pos:
tstl FPTEMP_HI(%a6) |check j bit
blts nden_exit |if set, not denorm
movew %d1,ETEMP(%a6) |input expected in ETEMP
movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
orl #unfl_bit,USER_FPSR(%a6) |set unfl
leal ETEMP(%a6),%a0
bra t_resdnrm
nden_exit:
movew %d1,FPTEMP(%a6) |result in FPTEMP
fmovel USER_FPCR(%a6),%FPCR
fmovex FPTEMP(%a6),%fp0 |write result to fp0
rts
|
| Source is negative. Add the src to the dest exponent.
| (The result exponent will be reduced). The result can be
| denormalized.
|
src_neg:
addl %d0,%d1 |add src to dest
beqs denorm |if zero, result is denorm
blts fix_dnrm |if negative, result is
| ;needing denormalization
tstb L_SCR1(%a6)
beqs sneg_pos
orw #0x8000,%d1
sneg_pos:
movew %d1,FPTEMP(%a6) |result in FPTEMP
fmovel USER_FPCR(%a6),%FPCR
fmovex FPTEMP(%a6),%fp0 |write result to fp0
rts
|
| The result exponent is below denorm value. Test for catastrophic
| underflow and force zero if true. If not, try to shift the
| mantissa right until a zero exponent exists.
|
fix_dnrm:
cmpiw #0xffc0,%d1 |lower bound for normalization
blt fix_unfl |if lower, catastrophic unfl
movew %d1,%d0 |use d0 for exp
movel %d2,-(%a7) |free d2 for norm
movel FPTEMP_HI(%a6),%d1
movel FPTEMP_LO(%a6),%d2
clrl L_SCR2(%a6)
fix_loop:
addw #1,%d0 |drive d0 to 0
lsrl #1,%d1 |while shifting the
roxrl #1,%d2 |mantissa to the right
bccs no_carry
st L_SCR2(%a6) |use L_SCR2 to capture inex
no_carry:
tstw %d0 |it is finished when
blts fix_loop |d0 is zero or the mantissa
tstb L_SCR2(%a6)
beqs tst_zero
orl #unfl_inx_mask,USER_FPSR(%a6)
| ;set unfl, aunfl, ainex
|
| Test for zero. If zero, simply use fmove to return +/- zero
| to the fpu.
|
tst_zero:
clrw FPTEMP_EX(%a6)
tstb L_SCR1(%a6) |test for sign
beqs tst_con
orw #0x8000,FPTEMP_EX(%a6) |set sign bit
tst_con:
movel %d1,FPTEMP_HI(%a6)
movel %d2,FPTEMP_LO(%a6)
movel (%a7)+,%d2
tstl %d1
bnes not_zero
tstl FPTEMP_LO(%a6)
bnes not_zero
|
| Result is zero. Check for rounding mode to set lsb. If the
| mode is rp, and the zero is positive, return smallest denorm.
| If the mode is rm, and the zero is negative, return smallest
| negative denorm.
|
btstb #5,FPCR_MODE(%a6) |test if rm or rp
beqs no_dir
btstb #4,FPCR_MODE(%a6) |check which one
beqs zer_rm
zer_rp:
tstb L_SCR1(%a6) |check sign
bnes no_dir |if set, neg op, no inc
movel #1,FPTEMP_LO(%a6) |set lsb
bras sm_dnrm
zer_rm:
tstb L_SCR1(%a6) |check sign
beqs no_dir |if clr, neg op, no inc
movel #1,FPTEMP_LO(%a6) |set lsb
orl #neg_mask,USER_FPSR(%a6) |set N
bras sm_dnrm
no_dir:
fmovel USER_FPCR(%a6),%FPCR
fmovex FPTEMP(%a6),%fp0 |use fmove to set cc's
rts
|
| The rounding mode changed the zero to a smallest denorm. Call
| t_resdnrm with exceptional operand in ETEMP.
|
sm_dnrm:
movel FPTEMP_EX(%a6),ETEMP_EX(%a6)
movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
leal ETEMP(%a6),%a0
bra t_resdnrm
|
| Result is still denormalized.
|
not_zero:
orl #unfl_mask,USER_FPSR(%a6) |set unfl
tstb L_SCR1(%a6) |check for sign
beqs fix_exit
orl #neg_mask,USER_FPSR(%a6) |set N
fix_exit:
bras sm_dnrm
|
| The result has underflowed to zero. Return zero and set
| unfl, aunfl, and ainex.
|
fix_unfl:
orl #unfl_inx_mask,USER_FPSR(%a6)
btstb #5,FPCR_MODE(%a6) |test if rm or rp
beqs no_dir2
btstb #4,FPCR_MODE(%a6) |check which one
beqs zer_rm2
zer_rp2:
tstb L_SCR1(%a6) |check sign
bnes no_dir2 |if set, neg op, no inc
clrl FPTEMP_EX(%a6)
clrl FPTEMP_HI(%a6)
movel #1,FPTEMP_LO(%a6) |set lsb
bras sm_dnrm |return smallest denorm
zer_rm2:
tstb L_SCR1(%a6) |check sign
beqs no_dir2 |if clr, neg op, no inc
movew #0x8000,FPTEMP_EX(%a6)
clrl FPTEMP_HI(%a6)
movel #1,FPTEMP_LO(%a6) |set lsb
orl #neg_mask,USER_FPSR(%a6) |set N
bra sm_dnrm |return smallest denorm
no_dir2:
tstb L_SCR1(%a6)
bges pos_zero
neg_zero:
clrl FP_SCR1(%a6) |clear the exceptional operand
clrl FP_SCR1+4(%a6) |for gen_except.
clrl FP_SCR1+8(%a6)
fmoves #0x80000000,%fp0
rts
pos_zero:
clrl FP_SCR1(%a6) |clear the exceptional operand
clrl FP_SCR1+4(%a6) |for gen_except.
clrl FP_SCR1+8(%a6)
fmoves #0x00000000,%fp0
rts
|
| The destination is a denormalized number. It must be handled
| by first shifting the bits in the mantissa until it is normalized,
| then adding the remainder of the source to the exponent.
|
dst_dnrm:
moveml %d2/%d3,-(%a7)
movew FPTEMP_EX(%a6),%d1
movel FPTEMP_HI(%a6),%d2
movel FPTEMP_LO(%a6),%d3
dst_loop:
tstl %d2 |test for normalized result
blts dst_norm |exit loop if so
tstl %d0 |otherwise, test shift count
beqs dst_fin |if zero, shifting is done
subil #1,%d0 |dec src
lsll #1,%d3
roxll #1,%d2
bras dst_loop
|
| Destination became normalized. Simply add the remaining
| portion of the src to the exponent.
|
dst_norm:
addw %d0,%d1 |dst is normalized; add src
tstb L_SCR1(%a6)
beqs dnrm_pos
orl #0x8000,%d1
dnrm_pos:
movemw %d1,FPTEMP_EX(%a6)
moveml %d2,FPTEMP_HI(%a6)
moveml %d3,FPTEMP_LO(%a6)
fmovel USER_FPCR(%a6),%FPCR
fmovex FPTEMP(%a6),%fp0
moveml (%a7)+,%d2/%d3
rts
|
| Destination remained denormalized. Call t_excdnrm with
| exceptional operand in ETEMP.
|
dst_fin:
tstb L_SCR1(%a6) |check for sign
beqs dst_exit
orl #neg_mask,USER_FPSR(%a6) |set N
orl #0x8000,%d1
dst_exit:
movemw %d1,ETEMP_EX(%a6)
moveml %d2,ETEMP_HI(%a6)
moveml %d3,ETEMP_LO(%a6)
orl #unfl_mask,USER_FPSR(%a6) |set unfl
moveml (%a7)+,%d2/%d3
leal ETEMP(%a6),%a0
bra t_resdnrm
|
| Source is outside of 2^14 range. Test the sign and branch
| to the appropriate exception handler.
|
src_out:
tstb L_SCR1(%a6)
beqs scro_pos
orl #0x8000,%d1
scro_pos:
movel FPTEMP_HI(%a6),ETEMP_HI(%a6)
movel FPTEMP_LO(%a6),ETEMP_LO(%a6)
tstw ETEMP(%a6)
blts res_neg
res_pos:
movew %d1,ETEMP(%a6) |result in ETEMP
bra t_ovfl2
res_neg:
movew %d1,ETEMP(%a6) |result in ETEMP
leal ETEMP(%a6),%a0
bra t_unfl
|end
|
