1 .file "reg_u_div.S"
2 /*---------------------------------------------------------------------------+ 3 | reg_u_div.S | 4 | | 5 | Core division routines | 6 | | 7 | Copyright (C) 1992,1993 | 8 | W. Metzenthen, 22 Parker St, Ormond, Vic 3163, | 9 | Australia. E-mail billm@vaxc.cc.monash.edu.au | 10 | | 11 | | 12 +---------------------------------------------------------------------------*/ 13
14 /*---------------------------------------------------------------------------+ 15 | Kernel for the division routines. | 16 | | 17 | void reg_u_div(FPU_REG *a, FPU_REG *a, | 18 | FPU_REG *dest, unsigned int control_word) | 19 | | 20 | Does not compute the destination exponent, but does adjust it. | 21 +---------------------------------------------------------------------------*/ 22
23 #include "exception.h"
24 #include "fpu_asm.h"
25 #include "control_w.h"
26
27
28 /* #define dSIGL(x) (x) */ 29 /* #define dSIGH(x) 4(x) */ 30
31
32 #ifndefNON_REENTRANT_FPU 33 /* 34 Local storage on the stack: 35 Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0 36 Overflow flag: ovfl_flag 37 */ 38 #define FPU_accum_3 -4(%ebp)
39 #define FPU_accum_2 -8(%ebp)
40 #define FPU_accum_1 -12(%ebp)
41 #define FPU_accum_0 -16(%ebp)
42 #define FPU_result_1 -20(%ebp)
43 #define FPU_result_2 -24(%ebp)
44 #define FPU_ovfl_flag -28(%ebp)
45
46 #else 47 .data
48 /* 49 Local storage in a static area: 50 Result: FPU_accum_3:FPU_accum_2:FPU_accum_1:FPU_accum_0 51 Overflow flag: ovfl_flag 52 */ 53 .align 2,0
54 FPU_accum_3:
55 .long 0
56 FPU_accum_2:
57 .long 0
58 FPU_accum_1:
59 .long 0
60 FPU_accum_0:
61 .long 0
62 FPU_result_1:
63 .long 0
64 FPU_result_2:
65 .long 0
66 FPU_ovfl_flag:
67 .byte 0
68 #endif NON_REENTRANT_FPU
69
70
71 .text
72 ENTRY(reg_u_div)
73 pushl %ebp
74 movl %esp,%ebp
75 #ifndefNON_REENTRANT_FPU 76 subl $28,%esp
77 #endif NON_REENTRANT_FPU
78
79 pushl %esi
80 pushl %edi
81 pushl %ebx
82
83 movl PARAM1,%esi /* pointer to num */ 84 movl PARAM2,%ebx /* pointer to denom */ 85 movl PARAM3,%edi /* pointer to answer */ 86
87 #ifdefDENORM_OPERAND 88 movl EXP(%esi),%eax
89 cmpl EXP_UNDER,%eax
90 jg xOp1_not_denorm
91
92 call SYMBOL_NAME(denormal_operand)
93 orl %eax,%eax
94 jnz fpu_Arith_exit
95
96 xOp1_not_denorm:
97 movl EXP(%ebx),%eax
98 cmpl EXP_UNDER,%eax
99 jg xOp2_not_denorm
100
101 call SYMBOL_NAME(denormal_operand)
102 orl %eax,%eax
103 jnz fpu_Arith_exit
104
105 xOp2_not_denorm:
106 #endif DENORM_OPERAND
107
108 ENTRY(divide_kernel)
109 #ifdefPARANOID 110 /* testl $0x80000000, SIGH(%esi) // Dividend */ 111 /* je L_bugged */ 112 testl $0x80000000, SIGH(%ebx) /* Divisor */ 113 je L_bugged
114 #endif PARANOID
115
116 /* Check if the divisor can be treated as having just 32 bits */ 117 cmpl $0,SIGL(%ebx)
118 jnz L_Full_Division /* Can't do a quick divide */ 119
120 /* We should be able to zip through the division here */ 121 movl SIGH(%ebx),%ecx /* The divisor */ 122 movl SIGH(%esi),%edx /* Dividend */ 123 movl SIGL(%esi),%eax /* Dividend */ 124
125 cmpl %ecx,%edx
126 setaeb FPU_ovfl_flag /* Keep a record */ 127 jb L_no_adjust
128
129 subl %ecx,%edx /* Prevent the overflow */ 130
131 L_no_adjust:
132 /* Divide the 64 bit number by the 32 bit denominator */ 133 divl %ecx
134 movl %eax,FPU_result_2
135
136 /* Work on the remainder of the first division */ 137 xorl %eax,%eax
138 divl %ecx
139 movl %eax,FPU_result_1
140
141 /* Work on the remainder of the 64 bit division */ 142 xorl %eax,%eax
143 divl %ecx
144
145 testb $255,FPU_ovfl_flag /* was the num > denom ? */ 146 je L_no_overflow
147
148 /* Do the shifting here */ 149 /* increase the exponent */ 150 incl EXP(%edi)
151
152 /* shift the mantissa right one bit */ 153 stc /* To set the ms bit */ 154 rcrl FPU_result_2
155 rcrl FPU_result_1
156 rcrl %eax
157
158 L_no_overflow:
159 jmp LRound_precision /* Do the rounding as required */ 160
161
162 /*---------------------------------------------------------------------------+ 163 | Divide: Return arg1/arg2 to arg3. | 164 | | 165 | This routine does not use the exponents of arg1 and arg2, but does | 166 | adjust the exponent of arg3. | 167 | | 168 | The maximum returned value is (ignoring exponents) | 169 | .ffffffff ffffffff | 170 | ------------------ = 1.ffffffff fffffffe | 171 | .80000000 00000000 | 172 | and the minimum is | 173 | .80000000 00000000 | 174 | ------------------ = .80000000 00000001 (rounded) | 175 | .ffffffff ffffffff | 176 | | 177 +---------------------------------------------------------------------------*/ 178
179
180 L_Full_Division:
181 /* Save extended dividend in local register */ 182 movl SIGL(%esi),%eax
183 movl %eax,FPU_accum_2
184 movl SIGH(%esi),%eax
185 movl %eax,FPU_accum_3
186 xorl %eax,%eax
187 movl %eax,FPU_accum_1 /* zero the extension */ 188 movl %eax,FPU_accum_0 /* zero the extension */ 189
190 movl SIGL(%esi),%eax /* Get the current num */ 191 movl SIGH(%esi),%edx
192
193 /*----------------------------------------------------------------------*/ 194 /* Initialization done. 195 Do the first 32 bits. */ 196
197 movb $0,FPU_ovfl_flag
198 cmpl SIGH(%ebx),%edx /* Test for imminent overflow */ 199 jb LLess_than_1
200 ja LGreater_than_1
201
202 cmpl SIGL(%ebx),%eax
203 jb LLess_than_1
204
205 LGreater_than_1:
206 /* The dividend is greater or equal, would cause overflow */ 207 setaeb FPU_ovfl_flag /* Keep a record */ 208
209 subl SIGL(%ebx),%eax
210 sbbl SIGH(%ebx),%edx /* Prevent the overflow */ 211 movl %eax,FPU_accum_2
212 movl %edx,FPU_accum_3
213
214 LLess_than_1:
215 /* At this point, we have a dividend < divisor, with a record of 216 adjustment in FPU_ovfl_flag */ 217
218 /* We will divide by a number which is too large */ 219 movl SIGH(%ebx),%ecx
220 addl $1,%ecx
221 jnc LFirst_div_not_1
222
223 /* here we need to divide by 100000000h, 224 i.e., no division at all.. */ 225 mov %edx,%eax
226 jmp LFirst_div_done
227
228 LFirst_div_not_1:
229 divl %ecx /* Divide the numerator by the augmented 230 denom ms dw */ 231
232 LFirst_div_done:
233 movl %eax,FPU_result_2 /* Put the result in the answer */ 234
235 mull SIGH(%ebx) /* mul by the ms dw of the denom */ 236
237 subl %eax,FPU_accum_2 /* Subtract from the num local reg */ 238 sbbl %edx,FPU_accum_3
239
240 movl FPU_result_2,%eax /* Get the result back */ 241 mull SIGL(%ebx) /* now mul the ls dw of the denom */ 242
243 subl %eax,FPU_accum_1 /* Subtract from the num local reg */ 244 sbbl %edx,FPU_accum_2
245 sbbl $0,FPU_accum_3
246 je LDo_2nd_32_bits /* Must check for non-zero result here */ 247
248 #ifdefPARANOID 249 jb L_bugged_1
250 #endif PARANOID
251
252 /* need to subtract another once of the denom */ 253 incl FPU_result_2 /* Correct the answer */ 254
255 movl SIGL(%ebx),%eax
256 movl SIGH(%ebx),%edx
257 subl %eax,FPU_accum_1 /* Subtract from the num local reg */ 258 sbbl %edx,FPU_accum_2
259
260 #ifdefPARANOID 261 sbbl $0,FPU_accum_3
262 jne L_bugged_1 /* Must check for non-zero result here */ 263 #endif PARANOID
264
265 /*----------------------------------------------------------------------*/ 266 /* Half of the main problem is done, there is just a reduced numerator 267 to handle now. 268 Work with the second 32 bits, FPU_accum_0 not used from now on */ 269 LDo_2nd_32_bits:
270 movl FPU_accum_2,%edx /* get the reduced num */ 271 movl FPU_accum_1,%eax
272
273 /* need to check for possible subsequent overflow */ 274 cmpl SIGH(%ebx),%edx
275 jb LDo_2nd_div
276 ja LPrevent_2nd_overflow
277
278 cmpl SIGL(%ebx),%eax
279 jb LDo_2nd_div
280
281 LPrevent_2nd_overflow:
282 /* The numerator is greater or equal, would cause overflow */ 283 /* prevent overflow */ 284 subl SIGL(%ebx),%eax
285 sbbl SIGH(%ebx),%edx
286 movl %edx,FPU_accum_2
287 movl %eax,FPU_accum_1
288
289 incl FPU_result_2 /* Reflect the subtraction in the answer */ 290
291 #ifdefPARANOID 292 je L_bugged_2 /* Can't bump the result to 1.0 */ 293 #endif PARANOID
294
295 LDo_2nd_div:
296 cmpl $0,%ecx /* augmented denom msw */ 297 jnz LSecond_div_not_1
298
299 /* %ecx == 0, we are dividing by 1.0 */ 300 mov %edx,%eax
301 jmp LSecond_div_done
302
303 LSecond_div_not_1:
304 divl %ecx /* Divide the numerator by the denom ms dw */ 305
306 LSecond_div_done:
307 movl %eax,FPU_result_1 /* Put the result in the answer */ 308
309 mull SIGH(%ebx) /* mul by the ms dw of the denom */ 310
311 subl %eax,FPU_accum_1 /* Subtract from the num local reg */ 312 sbbl %edx,FPU_accum_2
313
314 #ifdefPARANOID 315 jc L_bugged_2
316 #endif PARANOID
317
318 movl FPU_result_1,%eax /* Get the result back */ 319 mull SIGL(%ebx) /* now mul the ls dw of the denom */ 320
321 subl %eax,FPU_accum_0 /* Subtract from the num local reg */ 322 sbbl %edx,FPU_accum_1 /* Subtract from the num local reg */ 323 sbbl $0,FPU_accum_2
324
325 #ifdefPARANOID 326 jc L_bugged_2
327 #endif PARANOID
328
329 jz LDo_3rd_32_bits
330
331 #ifdefPARANOID 332 cmpl $1,FPU_accum_2
333 jne L_bugged_2
334 #endif PARANOID
335
336 /* need to subtract another once of the denom */ 337 movl SIGL(%ebx),%eax
338 movl SIGH(%ebx),%edx
339 subl %eax,FPU_accum_0 /* Subtract from the num local reg */ 340 sbbl %edx,FPU_accum_1
341 sbbl $0,FPU_accum_2
342
343 #ifdefPARANOID 344 jc L_bugged_2
345 jne L_bugged_2
346 #endif PARANOID
347
348 addl $1,FPU_result_1 /* Correct the answer */ 349 adcl $0,FPU_result_2
350
351 #ifdefPARANOID 352 jc L_bugged_2 /* Must check for non-zero result here */ 353 #endif PARANOID
354
355 /*----------------------------------------------------------------------*/ 356 /* The division is essentially finished here, we just need to perform 357 tidying operations. 358 Deal with the 3rd 32 bits */ 359 LDo_3rd_32_bits:
360 movl FPU_accum_1,%edx /* get the reduced num */ 361 movl FPU_accum_0,%eax
362
363 /* need to check for possible subsequent overflow */ 364 cmpl SIGH(%ebx),%edx /* denom */ 365 jb LRound_prep
366 ja LPrevent_3rd_overflow
367
368 cmpl SIGL(%ebx),%eax /* denom */ 369 jb LRound_prep
370
371 LPrevent_3rd_overflow:
372 /* prevent overflow */ 373 subl SIGL(%ebx),%eax
374 sbbl SIGH(%ebx),%edx
375 movl %edx,FPU_accum_1
376 movl %eax,FPU_accum_0
377
378 addl $1,FPU_result_1 /* Reflect the subtraction in the answer */ 379 adcl $0,FPU_result_2
380 jne LRound_prep
381 jnc LRound_prep
382
383 /* This is a tricky spot, there is an overflow of the answer */ 384 movb $255,FPU_ovfl_flag /* Overflow -> 1.000 */ 385
386 LRound_prep:
387 /* 388 * Prepare for rounding. 389 * To test for rounding, we just need to compare 2*accum with the 390 * denom. 391 */ 392 movl FPU_accum_0,%ecx
393 movl FPU_accum_1,%edx
394 movl %ecx,%eax
395 orl %edx,%eax
396 jz LRound_ovfl /* The accumulator contains zero. */ 397
398 /* Multiply by 2 */ 399 clc
400 rcll $1,%ecx
401 rcll $1,%edx
402 jc LRound_large /* No need to compare, denom smaller */ 403
404 subl SIGL(%ebx),%ecx
405 sbbl SIGH(%ebx),%edx
406 jnc LRound_not_small
407
408 movl $0x70000000,%eax /* Denom was larger */ 409 jmp LRound_ovfl
410
411 LRound_not_small:
412 jnz LRound_large
413
414 movl $0x80000000,%eax /* Remainder was exactly 1/2 denom */ 415 jmp LRound_ovfl
416
417 LRound_large:
418 movl $0xff000000,%eax /* Denom was smaller */ 419
420 LRound_ovfl:
421 /* We are now ready to deal with rounding, but first we must get 422 the bits properly aligned */ 423 testb $255,FPU_ovfl_flag /* was the num > denom ? */ 424 je LRound_precision
425
426 incl EXP(%edi)
427
428 /* shift the mantissa right one bit */ 429 stc /* Will set the ms bit */ 430 rcrl FPU_result_2
431 rcrl FPU_result_1
432 rcrl %eax
433
434 /* Round the result as required */ 435 LRound_precision:
436 decl EXP(%edi) /* binary point between 1st & 2nd bits */ 437
438 movl %eax,%edx
439 movl FPU_result_1,%ebx
440 movl FPU_result_2,%eax
441 jmp fpu_reg_round
442
443
444 #ifdefPARANOID 445 /* The logic is wrong if we got here */ 446 L_bugged:
447 pushl EX_INTERNAL|0x202
448 call EXCEPTION
449 pop %ebx
450 jmp L_exit
451
452 L_bugged_1:
453 pushl EX_INTERNAL|0x203
454 call EXCEPTION
455 pop %ebx
456 jmp L_exit
457
458 L_bugged_2:
459 pushl EX_INTERNAL|0x204
460 call EXCEPTION
461 pop %ebx
462 jmp L_exit
463
464 L_exit:
465 popl %ebx
466 popl %edi
467 popl %esi
468
469 leave
470 ret
471 #endif PARANOID
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