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