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/arch/parisc/math-emu/sfsub.c

https://github.com/aicjofs/android_kernel_lge_v500_20d_f2fs
C | 521 lines | 333 code | 23 blank | 165 comment | 69 complexity | 00a7366c26806e4e5fe46333c2907f70 MD5 | raw file
  1/*
  2 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
  3 *
  4 * Floating-point emulation code
  5 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
  6 *
  7 *    This program is free software; you can redistribute it and/or modify
  8 *    it under the terms of the GNU General Public License as published by
  9 *    the Free Software Foundation; either version 2, or (at your option)
 10 *    any later version.
 11 *
 12 *    This program is distributed in the hope that it will be useful,
 13 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 14 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 15 *    GNU General Public License for more details.
 16 *
 17 *    You should have received a copy of the GNU General Public License
 18 *    along with this program; if not, write to the Free Software
 19 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 20 */
 21/*
 22 * BEGIN_DESC
 23 *
 24 *  File:
 25 *	@(#)	pa/spmath/sfsub.c		$Revision: 1.1 $
 26 *
 27 *  Purpose:
 28 *	Single_subtract: subtract two single precision values.
 29 *
 30 *  External Interfaces:
 31 *	sgl_fsub(leftptr, rightptr, dstptr, status)
 32 *
 33 *  Internal Interfaces:
 34 *
 35 *  Theory:
 36 *	<<please update with a overview of the operation of this file>>
 37 *
 38 * END_DESC
 39*/
 40
 41
 42#include "float.h"
 43#include "sgl_float.h"
 44
 45/*
 46 * Single_subtract: subtract two single precision values.
 47 */
 48int
 49sgl_fsub(
 50	    sgl_floating_point *leftptr,
 51	    sgl_floating_point *rightptr,
 52	    sgl_floating_point *dstptr,
 53	    unsigned int *status)
 54    {
 55    register unsigned int left, right, result, extent;
 56    register unsigned int signless_upper_left, signless_upper_right, save;
 57    
 58    register int result_exponent, right_exponent, diff_exponent;
 59    register int sign_save, jumpsize;
 60    register boolean inexact = FALSE, underflowtrap;
 61        
 62    /* Create local copies of the numbers */
 63    left = *leftptr;
 64    right = *rightptr;
 65
 66    /* A zero "save" helps discover equal operands (for later),  *
 67     * and is used in swapping operands (if needed).             */
 68    Sgl_xortointp1(left,right,/*to*/save);
 69
 70    /*
 71     * check first operand for NaN's or infinity
 72     */
 73    if ((result_exponent = Sgl_exponent(left)) == SGL_INFINITY_EXPONENT)
 74	{
 75	if (Sgl_iszero_mantissa(left)) 
 76	    {
 77	    if (Sgl_isnotnan(right)) 
 78		{
 79		if (Sgl_isinfinity(right) && save==0) 
 80		    {
 81		    /* 
 82		     * invalid since operands are same signed infinity's
 83		     */
 84		    if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
 85                    Set_invalidflag();
 86                    Sgl_makequietnan(result);
 87		    *dstptr = result;
 88		    return(NOEXCEPTION);
 89		    }
 90		/*
 91	 	 * return infinity
 92	 	 */
 93		*dstptr = left;
 94		return(NOEXCEPTION);
 95		}
 96	    }
 97	else 
 98	    {
 99            /*
100             * is NaN; signaling or quiet?
101             */
102            if (Sgl_isone_signaling(left)) 
103		{
104               	/* trap if INVALIDTRAP enabled */
105		if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
106        	/* make NaN quiet */
107        	Set_invalidflag();
108        	Sgl_set_quiet(left);
109        	}
110	    /* 
111	     * is second operand a signaling NaN? 
112	     */
113	    else if (Sgl_is_signalingnan(right)) 
114		{
115        	/* trap if INVALIDTRAP enabled */
116               	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
117		/* make NaN quiet */
118		Set_invalidflag();
119		Sgl_set_quiet(right);
120		*dstptr = right;
121		return(NOEXCEPTION);
122		}
123	    /*
124 	     * return quiet NaN
125 	     */
126 	    *dstptr = left;
127 	    return(NOEXCEPTION);
128	    }
129	} /* End left NaN or Infinity processing */
130    /*
131     * check second operand for NaN's or infinity
132     */
133    if (Sgl_isinfinity_exponent(right)) 
134	{
135	if (Sgl_iszero_mantissa(right)) 
136	    {
137	    /* return infinity */
138	    Sgl_invert_sign(right);
139	    *dstptr = right;
140	    return(NOEXCEPTION);
141	    }
142        /*
143         * is NaN; signaling or quiet?
144         */
145        if (Sgl_isone_signaling(right)) 
146	    {
147            /* trap if INVALIDTRAP enabled */
148	    if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
149	    /* make NaN quiet */
150	    Set_invalidflag();
151	    Sgl_set_quiet(right);
152	    }
153	/*
154	 * return quiet NaN
155 	 */
156	*dstptr = right;
157	return(NOEXCEPTION);
158    	} /* End right NaN or Infinity processing */
159
160    /* Invariant: Must be dealing with finite numbers */
161
162    /* Compare operands by removing the sign */
163    Sgl_copytoint_exponentmantissa(left,signless_upper_left);
164    Sgl_copytoint_exponentmantissa(right,signless_upper_right);
165
166    /* sign difference selects sub or add operation. */
167    if(Sgl_ismagnitudeless(signless_upper_left,signless_upper_right))
168	{
169	/* Set the left operand to the larger one by XOR swap *
170	 *  First finish the first word using "save"          */
171	Sgl_xorfromintp1(save,right,/*to*/right);
172	Sgl_xorfromintp1(save,left,/*to*/left);
173	result_exponent = Sgl_exponent(left);
174	Sgl_invert_sign(left);
175	}
176    /* Invariant:  left is not smaller than right. */ 
177
178    if((right_exponent = Sgl_exponent(right)) == 0)
179        {
180	/* Denormalized operands.  First look for zeroes */
181	if(Sgl_iszero_mantissa(right)) 
182	    {
183	    /* right is zero */
184	    if(Sgl_iszero_exponentmantissa(left))
185		{
186		/* Both operands are zeros */
187		Sgl_invert_sign(right);
188		if(Is_rounding_mode(ROUNDMINUS))
189		    {
190		    Sgl_or_signs(left,/*with*/right);
191		    }
192		else
193		    {
194		    Sgl_and_signs(left,/*with*/right);
195		    }
196		}
197	    else 
198		{
199		/* Left is not a zero and must be the result.  Trapped
200		 * underflows are signaled if left is denormalized.  Result
201		 * is always exact. */
202		if( (result_exponent == 0) && Is_underflowtrap_enabled() )
203		    {
204		    /* need to normalize results mantissa */
205	    	    sign_save = Sgl_signextendedsign(left);
206		    Sgl_leftshiftby1(left);
207		    Sgl_normalize(left,result_exponent);
208		    Sgl_set_sign(left,/*using*/sign_save);
209                    Sgl_setwrapped_exponent(left,result_exponent,unfl);
210		    *dstptr = left;
211		    /* inexact = FALSE */
212		    return(UNDERFLOWEXCEPTION);
213		    }
214		}
215	    *dstptr = left;
216	    return(NOEXCEPTION);
217	    }
218
219	/* Neither are zeroes */
220	Sgl_clear_sign(right);	/* Exponent is already cleared */
221	if(result_exponent == 0 )
222	    {
223	    /* Both operands are denormalized.  The result must be exact
224	     * and is simply calculated.  A sum could become normalized and a
225	     * difference could cancel to a true zero. */
226	    if( (/*signed*/int) save >= 0 )
227		{
228		Sgl_subtract(left,/*minus*/right,/*into*/result);
229		if(Sgl_iszero_mantissa(result))
230		    {
231		    if(Is_rounding_mode(ROUNDMINUS))
232			{
233			Sgl_setone_sign(result);
234			}
235		    else
236			{
237			Sgl_setzero_sign(result);
238			}
239		    *dstptr = result;
240		    return(NOEXCEPTION);
241		    }
242		}
243	    else
244		{
245		Sgl_addition(left,right,/*into*/result);
246		if(Sgl_isone_hidden(result))
247		    {
248		    *dstptr = result;
249		    return(NOEXCEPTION);
250		    }
251		}
252	    if(Is_underflowtrap_enabled())
253		{
254		/* need to normalize result */
255	    	sign_save = Sgl_signextendedsign(result);
256		Sgl_leftshiftby1(result);
257		Sgl_normalize(result,result_exponent);
258		Sgl_set_sign(result,/*using*/sign_save);
259                Sgl_setwrapped_exponent(result,result_exponent,unfl);
260		*dstptr = result;
261		/* inexact = FALSE */
262		return(UNDERFLOWEXCEPTION);
263		}
264	    *dstptr = result;
265	    return(NOEXCEPTION);
266	    }
267	right_exponent = 1;	/* Set exponent to reflect different bias
268				 * with denomalized numbers. */
269	}
270    else
271	{
272	Sgl_clear_signexponent_set_hidden(right);
273	}
274    Sgl_clear_exponent_set_hidden(left);
275    diff_exponent = result_exponent - right_exponent;
276
277    /* 
278     * Special case alignment of operands that would force alignment 
279     * beyond the extent of the extension.  A further optimization
280     * could special case this but only reduces the path length for this
281     * infrequent case.
282     */
283    if(diff_exponent > SGL_THRESHOLD)
284	{
285	diff_exponent = SGL_THRESHOLD;
286	}
287    
288    /* Align right operand by shifting to right */
289    Sgl_right_align(/*operand*/right,/*shifted by*/diff_exponent,
290      /*and lower to*/extent);
291
292    /* Treat sum and difference of the operands separately. */
293    if( (/*signed*/int) save >= 0 )
294	{
295	/*
296	 * Difference of the two operands.  Their can be no overflow.  A
297	 * borrow can occur out of the hidden bit and force a post
298	 * normalization phase.
299	 */
300	Sgl_subtract_withextension(left,/*minus*/right,/*with*/extent,/*into*/result);
301	if(Sgl_iszero_hidden(result))
302	    {
303	    /* Handle normalization */
304	    /* A straightforward algorithm would now shift the result
305	     * and extension left until the hidden bit becomes one.  Not
306	     * all of the extension bits need participate in the shift.
307	     * Only the two most significant bits (round and guard) are
308	     * needed.  If only a single shift is needed then the guard
309	     * bit becomes a significant low order bit and the extension
310	     * must participate in the rounding.  If more than a single 
311	     * shift is needed, then all bits to the right of the guard 
312	     * bit are zeros, and the guard bit may or may not be zero. */
313	    sign_save = Sgl_signextendedsign(result);
314            Sgl_leftshiftby1_withextent(result,extent,result);
315
316            /* Need to check for a zero result.  The sign and exponent
317	     * fields have already been zeroed.  The more efficient test
318	     * of the full object can be used.
319	     */
320    	    if(Sgl_iszero(result))
321		/* Must have been "x-x" or "x+(-x)". */
322		{
323		if(Is_rounding_mode(ROUNDMINUS)) Sgl_setone_sign(result);
324		*dstptr = result;
325		return(NOEXCEPTION);
326		}
327	    result_exponent--;
328	    /* Look to see if normalization is finished. */
329	    if(Sgl_isone_hidden(result))
330		{
331		if(result_exponent==0)
332		    {
333		    /* Denormalized, exponent should be zero.  Left operand *
334 		     * was normalized, so extent (guard, round) was zero    */
335		    goto underflow;
336		    }
337		else
338		    {
339		    /* No further normalization is needed. */
340		    Sgl_set_sign(result,/*using*/sign_save);
341	    	    Ext_leftshiftby1(extent);
342		    goto round;
343		    }
344		}
345
346	    /* Check for denormalized, exponent should be zero.  Left    *
347	     * operand was normalized, so extent (guard, round) was zero */
348	    if(!(underflowtrap = Is_underflowtrap_enabled()) &&
349	       result_exponent==0) goto underflow;
350
351	    /* Shift extension to complete one bit of normalization and
352	     * update exponent. */
353	    Ext_leftshiftby1(extent);
354
355	    /* Discover first one bit to determine shift amount.  Use a
356	     * modified binary search.  We have already shifted the result
357	     * one position right and still not found a one so the remainder
358	     * of the extension must be zero and simplifies rounding. */
359	    /* Scan bytes */
360	    while(Sgl_iszero_hiddenhigh7mantissa(result))
361		{
362		Sgl_leftshiftby8(result);
363		if((result_exponent -= 8) <= 0  && !underflowtrap)
364		    goto underflow;
365		}
366	    /* Now narrow it down to the nibble */
367	    if(Sgl_iszero_hiddenhigh3mantissa(result))
368		{
369		/* The lower nibble contains the normalizing one */
370		Sgl_leftshiftby4(result);
371		if((result_exponent -= 4) <= 0 && !underflowtrap)
372		    goto underflow;
373		}
374	    /* Select case were first bit is set (already normalized)
375	     * otherwise select the proper shift. */
376	    if((jumpsize = Sgl_hiddenhigh3mantissa(result)) > 7)
377		{
378		/* Already normalized */
379		if(result_exponent <= 0) goto underflow;
380		Sgl_set_sign(result,/*using*/sign_save);
381		Sgl_set_exponent(result,/*using*/result_exponent);
382		*dstptr = result;
383		return(NOEXCEPTION);
384		}
385	    Sgl_sethigh4bits(result,/*using*/sign_save);
386	    switch(jumpsize) 
387		{
388		case 1:
389		    {
390		    Sgl_leftshiftby3(result);
391		    result_exponent -= 3;
392		    break;
393		    }
394		case 2:
395		case 3:
396		    {
397		    Sgl_leftshiftby2(result);
398		    result_exponent -= 2;
399		    break;
400		    }
401		case 4:
402		case 5:
403		case 6:
404		case 7:
405		    {
406		    Sgl_leftshiftby1(result);
407		    result_exponent -= 1;
408		    break;
409		    }
410		}
411	    if(result_exponent > 0) 
412		{
413		Sgl_set_exponent(result,/*using*/result_exponent);
414		*dstptr = result;	/* Sign bit is already set */
415		return(NOEXCEPTION);
416		}
417	    /* Fixup potential underflows */
418	  underflow:
419	    if(Is_underflowtrap_enabled())
420		{
421		Sgl_set_sign(result,sign_save);
422                Sgl_setwrapped_exponent(result,result_exponent,unfl);
423		*dstptr = result;
424		/* inexact = FALSE */
425		return(UNDERFLOWEXCEPTION);
426		}
427	    /*
428	     * Since we cannot get an inexact denormalized result,
429	     * we can now return.
430	     */
431	    Sgl_right_align(result,/*by*/(1-result_exponent),extent);
432	    Sgl_clear_signexponent(result);
433	    Sgl_set_sign(result,sign_save);
434	    *dstptr = result;
435	    return(NOEXCEPTION);
436	    } /* end if(hidden...)... */
437	/* Fall through and round */
438	} /* end if(save >= 0)... */
439    else 
440	{
441	/* Add magnitudes */
442	Sgl_addition(left,right,/*to*/result);
443	if(Sgl_isone_hiddenoverflow(result))
444	    {
445	    /* Prenormalization required. */
446	    Sgl_rightshiftby1_withextent(result,extent,extent);
447	    Sgl_arithrightshiftby1(result);
448	    result_exponent++;
449	    } /* end if hiddenoverflow... */
450	} /* end else ...sub magnitudes... */
451    
452    /* Round the result.  If the extension is all zeros,then the result is
453     * exact.  Otherwise round in the correct direction.  No underflow is
454     * possible. If a postnormalization is necessary, then the mantissa is
455     * all zeros so no shift is needed. */
456  round:
457    if(Ext_isnotzero(extent))
458	{
459	inexact = TRUE;
460	switch(Rounding_mode())
461	    {
462	    case ROUNDNEAREST: /* The default. */
463	    if(Ext_isone_sign(extent))
464		{
465		/* at least 1/2 ulp */
466		if(Ext_isnotzero_lower(extent)  ||
467		  Sgl_isone_lowmantissa(result))
468		    {
469		    /* either exactly half way and odd or more than 1/2ulp */
470		    Sgl_increment(result);
471		    }
472		}
473	    break;
474
475	    case ROUNDPLUS:
476	    if(Sgl_iszero_sign(result))
477		{
478		/* Round up positive results */
479		Sgl_increment(result);
480		}
481	    break;
482	    
483	    case ROUNDMINUS:
484	    if(Sgl_isone_sign(result))
485		{
486		/* Round down negative results */
487		Sgl_increment(result);
488		}
489	    
490	    case ROUNDZERO:;
491	    /* truncate is simple */
492	    } /* end switch... */
493	if(Sgl_isone_hiddenoverflow(result)) result_exponent++;
494	}
495    if(result_exponent == SGL_INFINITY_EXPONENT)
496        {
497        /* Overflow */
498        if(Is_overflowtrap_enabled())
499	    {
500	    Sgl_setwrapped_exponent(result,result_exponent,ovfl);
501	    *dstptr = result;
502	    if (inexact)
503		if (Is_inexacttrap_enabled())
504		    return(OVERFLOWEXCEPTION | INEXACTEXCEPTION);
505		else Set_inexactflag();
506	    return(OVERFLOWEXCEPTION);
507	    }
508        else
509	    {
510	    Set_overflowflag();
511	    inexact = TRUE;
512	    Sgl_setoverflow(result);
513	    }
514	}
515    else Sgl_set_exponent(result,result_exponent);
516    *dstptr = result;
517    if(inexact) 
518	if(Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
519	else Set_inexactflag();
520    return(NOEXCEPTION);
521    }