📄 scale.s
字号:
//// $Id: scale.S,v 1.1 1998/12/14 23:15:25 joel Exp $//// 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to fp0.//// Modifies: fp0.//// Algorithm:// // Copyright (C) Motorola, Inc. 1990// All Rights Reserved//// THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA // The copyright notice above does not evidence any // actual or intended publication of such source code.//SCALE idnt 2,1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.defs" |xref t_ovfl2 |xref t_unfl |xref round |xref t_resdnrmSRC_BNDS: .short 0x3fff,0x400c//// This entry point is used by the unimplemented instruction exception// handler.//////// FSCALE// .global sscalesscale: 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 UNFLden_done: leal FPTEMP(%a6),%a0 bra t_resdnrmno_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,%d1spos_pos: movew %d1,FPTEMP(%a6) //result in FPTEMP fmovel USER_FPCR(%a6),%FPCR fmovex FPTEMP(%a6),%fp0 //write result to fp0 rtsovfl: tstb L_SCR1(%a6) beqs sovl_pos orw #0x8000,%d1sovl_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_ovfl2denorm: tstb L_SCR1(%a6) beqs den_pos orw #0x8000,%d1den_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_resdnrmnden_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,%d1sneg_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 inexno_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 bittst_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_rmzer_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_dnrmzer_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_dnrmno_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 Nfix_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_rm2zer_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 denormzer_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 denormno_dir2: tstb L_SCR1(%a6) bges pos_zeroneg_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 rtspos_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),%d3dst_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,%d1dnrm_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,%d1dst_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,%d1scro_pos: movel FPTEMP_HI(%a6),ETEMP_HI(%a6) movel FPTEMP_LO(%a6),ETEMP_LO(%a6) tstw ETEMP(%a6) blts res_negres_pos: movew %d1,ETEMP(%a6) //result in ETEMP bra t_ovfl2res_neg: movew %d1,ETEMP(%a6) //result in ETEMP leal ETEMP(%a6),%a0 bra t_unfl |end⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -