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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
+|
+| THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA
+| The copyright notice above does not evidence any
+| actual or intended publication of such source code.
+
+|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