1 | 2 | scale.sa 3.3 7/30/91 3 | 4 | The entry point sSCALE computes the destination operand 5 | scaled by the source operand. If the absolute value of 6 | the source operand is (>= 2^14) an overflow or underflow 7 | is returned. 8 | 9 | The entry point sscale is called from do_func to emulate 10 | the fscale unimplemented instruction. 11 | 12 | Input: Double-extended destination operand in FPTEMP, 13 | double-extended source operand in ETEMP. 14 | 15 | Output: The function returns scale(X,Y) to fp0. 16 | 17 | Modifies: fp0. 18 | 19 | Algorithm: 20 | 21 | Copyright (C) Motorola, Inc. 1990 22 | All Rights Reserved 23 | 24 | For details on the license for this file, please see the 25 | file, README, in this same directory. 26 27 |SCALE idnt 2,1 | Motorola 040 Floating Point Software Package 28 29 |section 8 30 31 #include "fpsp.h" 32 33 |xref t_ovfl2 34 |xref t_unfl 35 |xref round 36 |xref t_resdnrm 37 38 SRC_BNDS: .short 0x3fff,0x400c 39 40 | 41 | This entry point is used by the unimplemented instruction exception 42 | handler. 43 | 44 | 45 | 46 | FSCALE 47 | 48 .global sscale 49 sscale: 50 fmovel #0,%fpcr |clr user enabled exc 51 clrl %d1 52 movew FPTEMP(%a6),%d1 |get dest exponent 53 smi L_SCR1(%a6) |use L_SCR1 to hold sign 54 andil #0x7fff,%d1 |strip sign 55 movew ETEMP(%a6),%d0 |check src bounds 56 andiw #0x7fff,%d0 |clr sign bit 57 cmp2w SRC_BNDS,%d0 58 bccs src_in 59 cmpiw #0x400c,%d0 |test for too large 60 bge src_out 61 | 62 | The source input is below 1, so we check for denormalized numbers 63 | and set unfl. 64 | 65 src_small: 66 moveb DTAG(%a6),%d0 67 andib #0xe0,%d0 68 tstb %d0 69 beqs no_denorm 70 st STORE_FLG(%a6) |dest already contains result 71 orl #unfl_mask,USER_FPSR(%a6) |set UNFL 72 den_done: 73 leal FPTEMP(%a6),%a0 74 bra t_resdnrm 75 no_denorm: 76 fmovel USER_FPCR(%a6),%FPCR 77 fmovex FPTEMP(%a6),%fp0 |simply return dest 78 rts 79 80 81 | 82 | Source is within 2^14 range. To perform the int operation, 83 | move it to d0. 84 | 85 src_in: 86 fmovex ETEMP(%a6),%fp0 |move in src for int 87 fmovel #rz_mode,%fpcr |force rz for src conversion 88 fmovel %fp0,%d0 |int src to d0 89 fmovel #0,%FPSR |clr status from above 90 tstw ETEMP(%a6) |check src sign 91 blt src_neg 92 | 93 | Source is positive. Add the src to the dest exponent. 94 | The result can be denormalized, if src = 0, or overflow, 95 | if the result of the add sets a bit in the upper word. 96 | 97 src_pos: 98 tstw %d1 |check for denorm 99 beq dst_dnrm 100 addl %d0,%d1 |add src to dest exp 101 beqs denorm |if zero, result is denorm 102 cmpil #0x7fff,%d1 |test for overflow 103 bges ovfl 104 tstb L_SCR1(%a6) 105 beqs spos_pos 106 orw #0x8000,%d1 107 spos_pos: 108 movew %d1,FPTEMP(%a6) |result in FPTEMP 109 fmovel USER_FPCR(%a6),%FPCR 110 fmovex FPTEMP(%a6),%fp0 |write result to fp0 111 rts 112 ovfl: 113 tstb L_SCR1(%a6) 114 beqs sovl_pos 115 orw #0x8000,%d1 116 sovl_pos: 117 movew FPTEMP(%a6),ETEMP(%a6) |result in ETEMP 118 movel FPTEMP_HI(%a6),ETEMP_HI(%a6) 119 movel FPTEMP_LO(%a6),ETEMP_LO(%a6) 120 bra t_ovfl2 121 122 denorm: 123 tstb L_SCR1(%a6) 124 beqs den_pos 125 orw #0x8000,%d1 126 den_pos: 127 tstl FPTEMP_HI(%a6) |check j bit 128 blts nden_exit |if set, not denorm 129 movew %d1,ETEMP(%a6) |input expected in ETEMP 130 movel FPTEMP_HI(%a6),ETEMP_HI(%a6) 131 movel FPTEMP_LO(%a6),ETEMP_LO(%a6) 132 orl #unfl_bit,USER_FPSR(%a6) |set unfl 133 leal ETEMP(%a6),%a0 134 bra t_resdnrm 135 nden_exit: 136 movew %d1,FPTEMP(%a6) |result in FPTEMP 137 fmovel USER_FPCR(%a6),%FPCR 138 fmovex FPTEMP(%a6),%fp0 |write result to fp0 139 rts 140 141 | 142 | Source is negative. Add the src to the dest exponent. 143 | (The result exponent will be reduced). The result can be 144 | denormalized. 145 | 146 src_neg: 147 addl %d0,%d1 |add src to dest 148 beqs denorm |if zero, result is denorm 149 blts fix_dnrm |if negative, result is 150 | ;needing denormalization 151 tstb L_SCR1(%a6) 152 beqs sneg_pos 153 orw #0x8000,%d1 154 sneg_pos: 155 movew %d1,FPTEMP(%a6) |result in FPTEMP 156 fmovel USER_FPCR(%a6),%FPCR 157 fmovex FPTEMP(%a6),%fp0 |write result to fp0 158 rts 159 160 161 | 162 | The result exponent is below denorm value. Test for catastrophic 163 | underflow and force zero if true. If not, try to shift the 164 | mantissa right until a zero exponent exists. 165 | 166 fix_dnrm: 167 cmpiw #0xffc0,%d1 |lower bound for normalization 168 blt fix_unfl |if lower, catastrophic unfl 169 movew %d1,%d0 |use d0 for exp 170 movel %d2,-(%a7) |free d2 for norm 171 movel FPTEMP_HI(%a6),%d1 172 movel FPTEMP_LO(%a6),%d2 173 clrl L_SCR2(%a6) 174 fix_loop: 175 addw #1,%d0 |drive d0 to 0 176 lsrl #1,%d1 |while shifting the 177 roxrl #1,%d2 |mantissa to the right 178 bccs no_carry 179 st L_SCR2(%a6) |use L_SCR2 to capture inex 180 no_carry: 181 tstw %d0 |it is finished when 182 blts fix_loop |d0 is zero or the mantissa 183 tstb L_SCR2(%a6) 184 beqs tst_zero 185 orl #unfl_inx_mask,USER_FPSR(%a6) 186 | ;set unfl, aunfl, ainex 187 | 188 | Test for zero. If zero, simply use fmove to return +/- zero 189 | to the fpu. 190 | 191 tst_zero: 192 clrw FPTEMP_EX(%a6) 193 tstb L_SCR1(%a6) |test for sign 194 beqs tst_con 195 orw #0x8000,FPTEMP_EX(%a6) |set sign bit 196 tst_con: 197 movel %d1,FPTEMP_HI(%a6) 198 movel %d2,FPTEMP_LO(%a6) 199 movel (%a7)+,%d2 200 tstl %d1 201 bnes not_zero 202 tstl FPTEMP_LO(%a6) 203 bnes not_zero 204 | 205 | Result is zero. Check for rounding mode to set lsb. If the 206 | mode is rp, and the zero is positive, return smallest denorm. 207 | If the mode is rm, and the zero is negative, return smallest 208 | negative denorm. 209 | 210 btstb #5,FPCR_MODE(%a6) |test if rm or rp 211 beqs no_dir 212 btstb #4,FPCR_MODE(%a6) |check which one 213 beqs zer_rm 214 zer_rp: 215 tstb L_SCR1(%a6) |check sign 216 bnes no_dir |if set, neg op, no inc 217 movel #1,FPTEMP_LO(%a6) |set lsb 218 bras sm_dnrm 219 zer_rm: 220 tstb L_SCR1(%a6) |check sign 221 beqs no_dir |if clr, neg op, no inc 222 movel #1,FPTEMP_LO(%a6) |set lsb 223 orl #neg_mask,USER_FPSR(%a6) |set N 224 bras sm_dnrm 225 no_dir: 226 fmovel USER_FPCR(%a6),%FPCR 227 fmovex FPTEMP(%a6),%fp0 |use fmove to set cc's 228 rts 229 230 | 231 | The rounding mode changed the zero to a smallest denorm. Call 232 | t_resdnrm with exceptional operand in ETEMP. 233 | 234 sm_dnrm: 235 movel FPTEMP_EX(%a6),ETEMP_EX(%a6) 236 movel FPTEMP_HI(%a6),ETEMP_HI(%a6) 237 movel FPTEMP_LO(%a6),ETEMP_LO(%a6) 238 leal ETEMP(%a6),%a0 239 bra t_resdnrm 240 241 | 242 | Result is still denormalized. 243 | 244 not_zero: 245 orl #unfl_mask,USER_FPSR(%a6) |set unfl 246 tstb L_SCR1(%a6) |check for sign 247 beqs fix_exit 248 orl #neg_mask,USER_FPSR(%a6) |set N 249 fix_exit: 250 bras sm_dnrm 251 252 253 | 254 | The result has underflowed to zero. Return zero and set 255 | unfl, aunfl, and ainex. 256 | 257 fix_unfl: 258 orl #unfl_inx_mask,USER_FPSR(%a6) 259 btstb #5,FPCR_MODE(%a6) |test if rm or rp 260 beqs no_dir2 261 btstb #4,FPCR_MODE(%a6) |check which one 262 beqs zer_rm2 263 zer_rp2: 264 tstb L_SCR1(%a6) |check sign 265 bnes no_dir2 |if set, neg op, no inc 266 clrl FPTEMP_EX(%a6) 267 clrl FPTEMP_HI(%a6) 268 movel #1,FPTEMP_LO(%a6) |set lsb 269 bras sm_dnrm |return smallest denorm 270 zer_rm2: 271 tstb L_SCR1(%a6) |check sign 272 beqs no_dir2 |if clr, neg op, no inc 273 movew #0x8000,FPTEMP_EX(%a6) 274 clrl FPTEMP_HI(%a6) 275 movel #1,FPTEMP_LO(%a6) |set lsb 276 orl #neg_mask,USER_FPSR(%a6) |set N 277 bra sm_dnrm |return smallest denorm 278 279 no_dir2: 280 tstb L_SCR1(%a6) 281 bges pos_zero 282 neg_zero: 283 clrl FP_SCR1(%a6) |clear the exceptional operand 284 clrl FP_SCR1+4(%a6) |for gen_except. 285 clrl FP_SCR1+8(%a6) 286 fmoves #0x80000000,%fp0 287 rts 288 pos_zero: 289 clrl FP_SCR1(%a6) |clear the exceptional operand 290 clrl FP_SCR1+4(%a6) |for gen_except. 291 clrl FP_SCR1+8(%a6) 292 fmoves #0x00000000,%fp0 293 rts 294 295 | 296 | The destination is a denormalized number. It must be handled 297 | by first shifting the bits in the mantissa until it is normalized, 298 | then adding the remainder of the source to the exponent. 299 | 300 dst_dnrm: 301 moveml %d2/%d3,-(%a7) 302 movew FPTEMP_EX(%a6),%d1 303 movel FPTEMP_HI(%a6),%d2 304 movel FPTEMP_LO(%a6),%d3 305 dst_loop: 306 tstl %d2 |test for normalized result 307 blts dst_norm |exit loop if so 308 tstl %d0 |otherwise, test shift count 309 beqs dst_fin |if zero, shifting is done 310 subil #1,%d0 |dec src 311 lsll #1,%d3 312 roxll #1,%d2 313 bras dst_loop 314 | 315 | Destination became normalized. Simply add the remaining 316 | portion of the src to the exponent. 317 | 318 dst_norm: 319 addw %d0,%d1 |dst is normalized; add src 320 tstb L_SCR1(%a6) 321 beqs dnrm_pos 322 orl #0x8000,%d1 323 dnrm_pos: 324 movemw %d1,FPTEMP_EX(%a6) 325 moveml %d2,FPTEMP_HI(%a6) 326 moveml %d3,FPTEMP_LO(%a6) 327 fmovel USER_FPCR(%a6),%FPCR 328 fmovex FPTEMP(%a6),%fp0 329 moveml (%a7)+,%d2/%d3 330 rts 331 332 | 333 | Destination remained denormalized. Call t_excdnrm with 334 | exceptional operand in ETEMP. 335 | 336 dst_fin: 337 tstb L_SCR1(%a6) |check for sign 338 beqs dst_exit 339 orl #neg_mask,USER_FPSR(%a6) |set N 340 orl #0x8000,%d1 341 dst_exit: 342 movemw %d1,ETEMP_EX(%a6) 343 moveml %d2,ETEMP_HI(%a6) 344 moveml %d3,ETEMP_LO(%a6) 345 orl #unfl_mask,USER_FPSR(%a6) |set unfl 346 moveml (%a7)+,%d2/%d3 347 leal ETEMP(%a6),%a0 348 bra t_resdnrm 349 350 | 351 | Source is outside of 2^14 range. Test the sign and branch 352 | to the appropriate exception handler. 353 | 354 src_out: 355 tstb L_SCR1(%a6) 356 beqs scro_pos 357 orl #0x8000,%d1 358 scro_pos: 359 movel FPTEMP_HI(%a6),ETEMP_HI(%a6) 360 movel FPTEMP_LO(%a6),ETEMP_LO(%a6) 361 tstw ETEMP(%a6) 362 blts res_neg 363 res_pos: 364 movew %d1,ETEMP(%a6) |result in ETEMP 365 bra t_ovfl2 366 res_neg: 367 movew %d1,ETEMP(%a6) |result in ETEMP 368 leal ETEMP(%a6),%a0 369 bra t_unfl 370 |end