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370 lines
8.7 KiB
370 lines
8.7 KiB
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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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| |
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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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| |
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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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| |
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| Output: The function returns scale(X,Y) to fp0. |
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| |
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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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| |
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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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| |
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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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| |
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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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| |
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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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| |
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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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| |
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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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| |
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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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