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05780f4b MM |
1 | /* |
2 | * Matt McCutchen's Big Integer Library | |
3 | * http://mysite.verizon.net/mccutchen/bigint/ | |
4 | */ | |
5 | ||
6 | #include "BigUnsigned.hh" | |
7 | ||
8 | // The "management" routines that used to be here are now in NumberlikeArray.cpp. | |
9 | ||
10 | /* | |
11 | * The steps for construction of a BigUnsigned | |
12 | * from an integral value x are as follows: | |
13 | * 1. If x is zero, create an empty BigUnsigned and stop. | |
14 | * 2. If x is negative, throw an exception. | |
15 | * 3. Allocate a one-block number array. | |
16 | * 4. If x is of a signed type, convert x to the unsigned | |
17 | * type of the same length. | |
18 | * 5. Expand x to a Blk, and store it in the number array. | |
19 | */ | |
20 | ||
21 | BigUnsigned::BigUnsigned(unsigned long x) { | |
22 | if (x == 0) { | |
23 | cap = 0; | |
24 | blk = new Blk[0]; | |
25 | len = 0; | |
26 | } else { | |
27 | cap = 1; | |
28 | blk = new Blk[1]; | |
29 | len = 1; | |
30 | blk[0] = Blk(x); | |
31 | } | |
32 | } | |
33 | ||
34 | BigUnsigned::BigUnsigned(long x) { | |
35 | if (x == 0) { | |
36 | cap = 0; | |
37 | blk = new Blk[0]; | |
38 | len = 0; | |
39 | } else if (x > 0) { | |
40 | cap = 1; | |
41 | blk = new Blk[1]; | |
42 | len = 1; | |
43 | blk[0] = Blk(x); | |
44 | } else | |
45 | throw "BigUnsigned::BigUnsigned(long): Cannot construct a BigUnsigned from a negative number"; | |
46 | } | |
47 | ||
48 | BigUnsigned::BigUnsigned(unsigned int x) { | |
49 | if (x == 0) { | |
50 | cap = 0; | |
51 | blk = new Blk[0]; | |
52 | len = 0; | |
53 | } else { | |
54 | cap = 1; | |
55 | blk = new Blk[1]; | |
56 | len = 1; | |
57 | blk[0] = Blk(x); | |
58 | } | |
59 | } | |
60 | ||
61 | BigUnsigned::BigUnsigned(int x) { | |
62 | if (x == 0) { | |
63 | cap = 0; | |
64 | blk = new Blk[0]; | |
65 | len = 0; | |
66 | } else if (x > 0) { | |
67 | cap = 1; | |
68 | blk = new Blk[1]; | |
69 | len = 1; | |
70 | blk[0] = Blk(x); | |
71 | } else | |
72 | throw "BigUnsigned::BigUnsigned(int): Cannot construct a BigUnsigned from a negative number"; | |
73 | } | |
74 | ||
75 | BigUnsigned::BigUnsigned(unsigned short x) { | |
76 | if (x == 0) { | |
77 | cap = 0; | |
78 | blk = new Blk[0]; | |
79 | len = 0; | |
80 | } else { | |
81 | cap = 1; | |
82 | blk = new Blk[1]; | |
83 | len = 1; | |
84 | blk[0] = Blk(x); | |
85 | } | |
86 | } | |
87 | ||
88 | BigUnsigned::BigUnsigned(short x) { | |
89 | if (x == 0) { | |
90 | cap = 0; | |
91 | blk = new Blk[0]; | |
92 | len = 0; | |
93 | } else if (x > 0) { | |
94 | cap = 1; | |
95 | blk = new Blk[1]; | |
96 | len = 1; | |
97 | blk[0] = Blk(x); | |
98 | } else | |
99 | throw "BigUnsigned::BigUnsigned(short): Cannot construct a BigUnsigned from a negative number"; | |
100 | } | |
101 | ||
102 | // CONVERTERS | |
103 | /* | |
104 | * The steps for conversion of a BigUnsigned to an | |
105 | * integral type are as follows: | |
106 | * 1. If the BigUnsigned is zero, return zero. | |
107 | * 2. If it is more than one block long or its lowest | |
108 | * block has bits set out of the range of the target | |
109 | * type, throw an exception. | |
110 | * 3. Otherwise, convert the lowest block to the | |
111 | * target type and return it. | |
112 | */ | |
113 | ||
114 | namespace { | |
115 | // These masks are used to test whether a Blk has bits | |
116 | // set out of the range of a smaller integral type. Note | |
117 | // that this range is not considered to include the sign bit. | |
118 | const BigUnsigned::Blk lMask = ~0 >> 1; | |
119 | const BigUnsigned::Blk uiMask = (unsigned int)(~0); | |
120 | const BigUnsigned::Blk iMask = uiMask >> 1; | |
121 | const BigUnsigned::Blk usMask = (unsigned short)(~0); | |
122 | const BigUnsigned::Blk sMask = usMask >> 1; | |
123 | } | |
124 | ||
125 | BigUnsigned::operator unsigned long() const { | |
126 | if (len == 0) | |
127 | return 0; | |
128 | else if (len == 1) | |
129 | return (unsigned long) blk[0]; | |
130 | else | |
131 | throw "BigUnsigned::operator unsigned long: Value is too big for an unsigned long"; | |
132 | } | |
133 | ||
134 | BigUnsigned::operator long() const { | |
135 | if (len == 0) | |
136 | return 0; | |
137 | else if (len == 1 && (blk[0] & lMask) == blk[0]) | |
138 | return (long) blk[0]; | |
139 | else | |
140 | throw "BigUnsigned::operator long: Value is too big for a long"; | |
141 | } | |
142 | ||
143 | BigUnsigned::operator unsigned int() const { | |
144 | if (len == 0) | |
145 | return 0; | |
146 | else if (len == 1 && (blk[0] & uiMask) == blk[0]) | |
147 | return (unsigned int) blk[0]; | |
148 | else | |
149 | throw "BigUnsigned::operator unsigned int: Value is too big for an unsigned int"; | |
150 | } | |
151 | ||
152 | BigUnsigned::operator int() const { | |
153 | if (len == 0) | |
154 | return 0; | |
155 | else if (len == 1 && (blk[0] & iMask) == blk[0]) | |
156 | return (int) blk[0]; | |
157 | else | |
158 | throw "BigUnsigned::operator int: Value is too big for an int"; | |
159 | } | |
160 | ||
161 | BigUnsigned::operator unsigned short() const { | |
162 | if (len == 0) | |
163 | return 0; | |
164 | else if (len == 1 && (blk[0] & usMask) == blk[0]) | |
165 | return (unsigned short) blk[0]; | |
166 | else | |
167 | throw "BigUnsigned::operator unsigned short: Value is too big for an unsigned short"; | |
168 | } | |
169 | ||
170 | BigUnsigned::operator short() const { | |
171 | if (len == 0) | |
172 | return 0; | |
173 | else if (len == 1 && (blk[0] & sMask) == blk[0]) | |
174 | return (short) blk[0]; | |
175 | else | |
176 | throw "BigUnsigned::operator short: Value is too big for a short"; | |
177 | } | |
178 | ||
179 | // COMPARISON | |
180 | BigUnsigned::CmpRes BigUnsigned::compareTo(const BigUnsigned &x) const { | |
181 | // A bigger length implies a bigger number. | |
182 | if (len < x.len) | |
183 | return less; | |
184 | else if (len > x.len) | |
185 | return greater; | |
186 | else { | |
187 | // Compare blocks one by one from left to right. | |
188 | Index i = len; | |
189 | while (i > 0) { | |
190 | i--; | |
191 | if (blk[i] == x.blk[i]) | |
192 | continue; | |
193 | else if (blk[i] > x.blk[i]) | |
194 | return greater; | |
195 | else | |
196 | return less; | |
197 | } | |
198 | // If no blocks differed, the numbers are equal. | |
199 | return equal; | |
200 | } | |
201 | } | |
202 | ||
203 | // PUT-HERE OPERATIONS | |
204 | ||
205 | // Addition | |
206 | void BigUnsigned::add(const BigUnsigned &a, const BigUnsigned &b) { | |
207 | // Block unsafe calls | |
208 | if (this == &a || this == &b) | |
209 | throw "BigUnsigned::add: One of the arguments is the invoked object"; | |
210 | // If one argument is zero, copy the other. | |
211 | if (a.len == 0) { | |
212 | operator =(b); | |
213 | return; | |
214 | } else if (b.len == 0) { | |
215 | operator =(a); | |
216 | return; | |
217 | } | |
218 | // Carries in and out of an addition stage | |
219 | bool carryIn, carryOut; | |
220 | Blk temp; | |
221 | Index i; | |
222 | // a2 points to the longer input, b2 points to the shorter | |
223 | const BigUnsigned *a2, *b2; | |
224 | if (a.len >= b.len) { | |
225 | a2 = &a; | |
226 | b2 = &b; | |
227 | } else { | |
228 | a2 = &b; | |
229 | b2 = &a; | |
230 | } | |
231 | // Set prelimiary length and make room in this BigUnsigned | |
232 | len = a2->len + 1; | |
233 | allocate(len); | |
234 | // For each block index that is present in both inputs... | |
235 | for (i = 0, carryIn = false; i < b2->len; i++) { | |
236 | // Add input blocks | |
237 | temp = a2->blk[i] + b2->blk[i]; | |
238 | // If a rollover occurred, the result is less than either input. | |
239 | // This test is used many times in the BigUnsigned code. | |
240 | carryOut = (temp < a2->blk[i]); | |
241 | // If a carry was input, handle it | |
242 | if (carryIn) { | |
243 | temp++; | |
244 | carryOut |= (temp == 0); | |
245 | } | |
246 | blk[i] = temp; // Save the addition result | |
247 | carryIn = carryOut; // Pass the carry along | |
248 | } | |
249 | // If there is a carry left over, increase blocks until | |
250 | // one does not roll over. | |
251 | for (; i < a2->len && carryIn; i++) { | |
252 | temp = a2->blk[i] + 1; | |
253 | carryIn = (temp == 0); | |
254 | blk[i] = temp; | |
255 | } | |
256 | // If the carry was resolved but the larger number | |
257 | // still has blocks, copy them over. | |
258 | for (; i < a2->len; i++) | |
259 | blk[i] = a2->blk[i]; | |
260 | // Set the extra block if there's still a carry, decrease length otherwise | |
261 | if (carryIn) | |
262 | blk[i] = 1; | |
263 | else | |
264 | len--; | |
265 | } | |
266 | ||
267 | // Subtraction | |
268 | void BigUnsigned::subtract(const BigUnsigned &a, const BigUnsigned &b) { | |
269 | // Block unsafe calls | |
270 | if (this == &a || this == &b) | |
271 | throw "BigUnsigned::subtract: One of the arguments is the invoked object"; | |
272 | // If b is zero, copy a. If a is shorter than b, the result is negative. | |
273 | if (b.len == 0) { | |
274 | operator =(a); | |
275 | return; | |
276 | } else if (a.len < b.len) | |
277 | throw "BigUnsigned::subtract: Negative result in unsigned calculation"; | |
278 | bool borrowIn, borrowOut; | |
279 | Blk temp; | |
280 | Index i; | |
281 | // Set preliminary length and make room | |
282 | len = a.len; | |
283 | allocate(len); | |
284 | // For each block index that is present in both inputs... | |
285 | for (i = 0, borrowIn = false; i < b.len; i++) { | |
286 | temp = a.blk[i] - b.blk[i]; | |
287 | // If a reverse rollover occurred, the result is greater than the block from a. | |
288 | borrowOut = (temp > a.blk[i]); | |
289 | // Handle an incoming borrow | |
290 | if (borrowIn) { | |
291 | borrowOut |= (temp == 0); | |
292 | temp--; | |
293 | } | |
294 | blk[i] = temp; // Save the subtraction result | |
295 | borrowIn = borrowOut; // Pass the borrow along | |
296 | } | |
297 | // If there is a borrow left over, decrease blocks until | |
298 | // one does not reverse rollover. | |
299 | for (; i < a.len && borrowIn; i++) { | |
300 | borrowIn = (a.blk[i] == 0); | |
301 | blk[i] = a.blk[i] - 1; | |
302 | } | |
303 | // If there's still a borrow, the result is negative. | |
304 | // Throw an exception, but zero out this object first just in case. | |
305 | if (borrowIn) { | |
306 | len = 0; | |
307 | throw "BigUnsigned::subtract: Negative result in unsigned calculation"; | |
308 | } else // Copy over the rest of the blocks | |
309 | for (; i < a.len; i++) | |
310 | blk[i] = a.blk[i]; | |
311 | // Zap leading zeros | |
312 | zapLeadingZeros(); | |
313 | } | |
314 | ||
315 | // Multiplication | |
316 | void BigUnsigned::multiply(const BigUnsigned &a, const BigUnsigned &b) { | |
317 | // Block unsafe calls | |
318 | if (this == &a || this == &b) | |
319 | throw "BigUnsigned::multiply: One of the arguments is the invoked object"; | |
320 | // If either a or b is zero, set to zero. | |
321 | if (a.len == 0 || b.len == 0) { | |
322 | len = 0; | |
323 | return; | |
324 | } | |
325 | // Overall method: this = 0, then for each 1-bit of a, add b | |
326 | // to this shifted the appropriate amount. | |
327 | // Variables for the calculation | |
328 | Index i, j, k; | |
329 | unsigned int i2; | |
330 | Blk aBlk, bHigh, temp; | |
331 | bool carryIn, carryOut; | |
332 | // Set preliminary length and make room | |
333 | len = a.len + b.len; | |
334 | allocate(len); | |
335 | // Zero out this object | |
336 | for (i = 0; i < len; i++) | |
337 | blk[i] = 0; | |
338 | // For each block of the first number... | |
339 | for (i = 0; i < a.len; i++) { | |
340 | // For each 1-bit of that block... | |
341 | for (i2 = 0, aBlk = a.blk[i]; aBlk != 0; i2++, aBlk >>= 1) { | |
342 | if ((aBlk & 1) == 0) | |
343 | continue; | |
344 | /* Add b to this, shifted left i blocks and i2 bits. | |
345 | * j is the index in b, and k = i + j is the index in this. | |
346 | * The low bits of b.blk[j] are shifted and added to blk[k]. | |
347 | * bHigh is used to carry the high bits to the next addition. */ | |
348 | bHigh = 0; | |
349 | for (j = 0, k = i, carryIn = false; j < b.len; j++, k++) { | |
350 | temp = blk[k] + ((b.blk[j] << i2) | bHigh); | |
351 | carryOut = (temp < blk[k]); | |
352 | if (carryIn) { | |
353 | temp++; | |
354 | carryOut |= (temp == 0); | |
355 | } | |
356 | blk[k] = temp; | |
357 | carryIn = carryOut; | |
358 | bHigh = (i2 == 0) ? 0 : b.blk[j] >> (8 * sizeof(Blk) - i2); | |
359 | } | |
360 | temp = blk[k] + bHigh; | |
361 | carryOut = (temp < blk[k]); | |
362 | if (carryIn) { | |
363 | temp++; | |
364 | carryOut |= (temp == 0); | |
365 | } | |
366 | blk[k] = temp; | |
367 | carryIn = carryOut; | |
368 | k++; // Added by Matt 2004.12.23: Move to the next block. It belongs here (and there was a corresponding line in the division routine), but I'm not certain whether it ever matters. | |
369 | for (; carryIn; k++) { | |
370 | blk[k]++; | |
371 | carryIn = (blk[k] == 0); | |
372 | } | |
373 | } | |
374 | } | |
375 | // Zap possible leading zero | |
376 | if (blk[len - 1] == 0) | |
377 | len--; | |
378 | } | |
379 | ||
380 | /* | |
381 | * DIVISION WITH REMAINDER | |
382 | * The functionality of divide, modulo, and %= is included in this one monstrous call, | |
383 | * which deserves some explanation. | |
384 | * | |
385 | * The division *this / b is performed. | |
386 | * Afterwards, q has the quotient, and *this has the remainder. | |
387 | * Thus, a call is like q = *this / b, *this %= b. | |
388 | * | |
389 | * This seemingly bizarre pattern of inputs and outputs has a justification. The | |
390 | * ``put-here operations'' are supposed to be fast. Therefore, they accept inputs | |
391 | * and provide outputs in the most convenient places so that no value ever needs | |
392 | * to be copied in its entirety. That way, the client can perform exactly the | |
393 | * copying it needs depending on where the inputs are and where it wants the output. | |
394 | */ | |
395 | void BigUnsigned::divideWithRemainder(const BigUnsigned &b, BigUnsigned &q) { | |
396 | // Block unsafe calls | |
397 | if (this == &b || &q == &b || this == &q) | |
398 | throw "BigUnsigned::divideWithRemainder: Some two objects involved are the same"; | |
399 | ||
400 | /* | |
401 | * Note that the mathematical definition of mod (I'm trusting Knuth) is somewhat | |
402 | * different from the way the normal C++ % operator behaves in the case of division by 0. | |
403 | * This function does it Knuth's way. | |
404 | * | |
405 | * We let a / 0 == 0 (it doesn't matter) and a % 0 == a, no exceptions thrown. | |
406 | * This allows us to preserve both Knuth's demand that a mod 0 == a | |
407 | * and the useful property that (a / b) * b + (a % b) == a. | |
408 | */ | |
409 | if (b.len == 0) { | |
410 | q.len = 0; | |
411 | return; | |
412 | } | |
413 | ||
414 | /* | |
415 | * If *this.len < b.len, then *this < b, and we can be sure that b doesn't go into | |
416 | * *this at all. The quotient is 0 and *this is already the remainder (so leave it alone). | |
417 | */ | |
418 | if (len < b.len) { | |
419 | q.len = 0; | |
420 | return; | |
421 | } | |
422 | ||
423 | /* | |
424 | * At this point we know *this > b > 0. (Whew!) | |
425 | */ | |
426 | ||
427 | /* DEBUG * | |
428 | std::cout << "divideWithRemainder starting\n" | |
429 | << "length of dividend: " << len | |
430 | << "\nlast block of dividend: " << getBlock(0) | |
431 | << "\nlength of divisor: " << b.len | |
432 | << "\nlast block of divisor: " << b.getBlock(0) | |
433 | << std::endl; */ | |
434 | ||
435 | /* | |
436 | * Overall method: Subtract b, shifted varying amounts to | |
437 | * the left, from this, setting the bit in the quotient q | |
438 | * whenever the subtraction succeeds. Eventually q will contain the entire | |
439 | * quotient, and this will be left with the remainder. | |
440 | * | |
441 | * We use work2 to temporarily store the result of a subtraction. | |
442 | * But we don't even compute the i lowest blocks of the result, | |
443 | * because they are unaffected (we shift left i places). | |
444 | * */ | |
445 | // Variables for the calculation | |
446 | Index i, j, k; | |
447 | unsigned int i2; | |
448 | Blk bHigh, temp; | |
449 | bool borrowIn, borrowOut; | |
450 | ||
451 | // Make sure we have an extra zero block just past the value, | |
452 | // but don't increase the logical length. A shifted subtraction | |
453 | // (for example, subtracting 1 << 2 from 4) might stick into | |
454 | // this block. | |
455 | allocateAndCopy(len + 1); | |
456 | blk[len] = 0; | |
457 | ||
458 | // work2 holds part of the result of a subtraction. | |
459 | // (There's no work1. The name work2 is from a previous version.) | |
460 | Blk *work2 = new Blk[len]; | |
461 | ||
462 | // Set preliminary length for quotient and make room | |
463 | q.len = len - b.len + 1; | |
464 | q.allocate(q.len); | |
465 | // Zero out the quotient | |
466 | for (i = 0; i < q.len; i++) | |
467 | q.blk[i] = 0; | |
468 | ||
469 | // For each possible left-shift of b in blocks... | |
470 | i = q.len; | |
471 | while (i > 0) { | |
472 | i--; | |
473 | // For each possible left-shift of b in bits... | |
474 | q.blk[i] = 0; | |
475 | i2 = 8 * sizeof(Blk); | |
476 | while (i2 > 0) { | |
477 | i2--; | |
478 | /* | |
479 | * Subtract b, shifted left i blocks and i2 bits, from this. | |
480 | * and store the answer in work2. | |
481 | * | |
482 | * Compare this to the middle section of `multiply'. They | |
483 | * are in many ways analogous. | |
484 | */ | |
485 | bHigh = 0; | |
486 | for (j = 0, k = i, borrowIn = false; j < b.len; j++, k++) { | |
487 | temp = blk[k] - ((b.blk[j] << i2) | bHigh); | |
488 | borrowOut = (temp > blk[k]); | |
489 | if (borrowIn) { | |
490 | borrowOut |= (temp == 0); | |
491 | temp--; | |
492 | } | |
493 | work2[j] = temp; | |
494 | borrowIn = borrowOut; | |
495 | bHigh = (i2 == 0) ? 0 : b.blk[j] >> (8 * sizeof(Blk) - i2); | |
496 | } | |
497 | temp = blk[k] - bHigh; | |
498 | borrowOut = (temp > blk[k]); | |
499 | if (borrowIn) { | |
500 | borrowOut |= (temp == 0); | |
501 | temp--; | |
502 | } | |
503 | work2[j] = temp; | |
504 | borrowIn = borrowOut; | |
505 | j++; | |
506 | k++; | |
507 | for (; k < len && borrowIn; j++, k++) { | |
508 | borrowIn = (blk[k] == 0); | |
509 | work2[j] = blk[k] - 1; | |
510 | } | |
511 | /* If the subtraction was performed successfully (!borrowIn), set bit i2 | |
512 | * in block i of the quotient, and copy the changed portion of | |
513 | * work2 back to this. Otherwise, reset that bit and move on. */ | |
514 | if (!borrowIn) { | |
515 | q.blk[i] |= (1 << i2); | |
516 | while (j > 0) { | |
517 | j--; | |
518 | k--; | |
519 | blk[k] = work2[j]; | |
520 | } | |
521 | } | |
522 | } | |
523 | } | |
524 | // Zap possible leading zero in quotient | |
525 | if (q.blk[q.len - 1] == 0) | |
526 | q.len--; | |
527 | // Zap any/all leading zeros in remainder | |
528 | zapLeadingZeros(); | |
529 | // Deallocate temporary array. | |
530 | // (Thanks to Brad Spencer for noticing my accidental omission of this!) | |
531 | delete [] work2; | |
532 | ||
533 | /* DEBUG * | |
534 | std::cout << "divideWithRemainder complete\n" | |
535 | << "length of quotient: " << q.len | |
536 | << "\nlast block of quotient: " << q.getBlock(0) | |
537 | << "\nlength of remainder: " << len | |
538 | << "\nlast block of remainder: " << getBlock(0) | |
539 | << std::endl; */ | |
540 | } | |
541 | ||
542 | // Bitwise and | |
543 | void BigUnsigned::bitAnd(const BigUnsigned &a, const BigUnsigned &b) { | |
544 | // Block unsafe calls | |
545 | if (this == &a || this == &b) | |
546 | throw "BigUnsigned::bitAnd: One of the arguments is the invoked object"; | |
547 | len = (a.len >= b.len) ? b.len : a.len; | |
548 | allocate(len); | |
549 | Index i; | |
550 | for (i = 0; i < len; i++) | |
551 | blk[i] = a.blk[i] & b.blk[i]; | |
552 | zapLeadingZeros(); | |
553 | } | |
554 | ||
555 | // Bitwise or | |
556 | void BigUnsigned::bitOr(const BigUnsigned &a, const BigUnsigned &b) { | |
557 | // Block unsafe calls | |
558 | if (this == &a || this == &b) | |
559 | throw "BigUnsigned::bitOr: One of the arguments is the invoked object"; | |
560 | Index i; | |
561 | const BigUnsigned *a2, *b2; | |
562 | if (a.len >= b.len) { | |
563 | a2 = &a; | |
564 | b2 = &b; | |
565 | } else { | |
566 | a2 = &b; | |
567 | b2 = &a; | |
568 | } | |
569 | allocate(a2->len); | |
570 | for (i = 0; i < b2->len; i++) | |
571 | blk[i] = a2->blk[i] | b2->blk[i]; | |
572 | for (; i < a2->len; i++) | |
573 | blk[i] = a2->blk[i]; | |
574 | len = a2->len; | |
575 | } | |
576 | ||
577 | // Bitwise xor | |
578 | void BigUnsigned::bitXor(const BigUnsigned &a, const BigUnsigned &b) { | |
579 | // Block unsafe calls | |
580 | if (this == &a || this == &b) | |
581 | throw "BigUnsigned::bitXor: One of the arguments is the invoked object"; | |
582 | Index i; | |
583 | const BigUnsigned *a2, *b2; | |
584 | if (a.len >= b.len) { | |
585 | a2 = &a; | |
586 | b2 = &b; | |
587 | } else { | |
588 | a2 = &b; | |
589 | b2 = &a; | |
590 | } | |
591 | allocate(b2->len); | |
592 | for (i = 0; i < b2->len; i++) | |
593 | blk[i] = a2->blk[i] ^ b2->blk[i]; | |
594 | for (; i < a2->len; i++) | |
595 | blk[i] = a2->blk[i]; | |
596 | len = a2->len; | |
597 | zapLeadingZeros(); | |
598 | } | |
599 | ||
600 | // INCREMENT/DECREMENT OPERATORS | |
601 | ||
602 | // Prefix increment | |
603 | void BigUnsigned::operator ++() { | |
604 | Index i; | |
605 | bool carry = true; | |
606 | for (i = 0; i < len && carry; i++) { | |
607 | blk[i]++; | |
608 | carry = (blk[i] == 0); | |
609 | } | |
610 | if (carry) { | |
611 | // Matt fixed a bug 2004.12.24: next 2 lines used to say allocateAndCopy(len + 1) | |
612 | len++; | |
613 | allocateAndCopy(len); | |
614 | blk[i] = 1; | |
615 | } | |
616 | } | |
617 | ||
618 | // Postfix increment: same as prefix | |
619 | void BigUnsigned::operator ++(int) { | |
620 | operator ++(); | |
621 | } | |
622 | ||
623 | // Prefix decrement | |
624 | void BigUnsigned::operator --() { | |
625 | if (len == 0) | |
626 | throw "BigUnsigned::operator --(): Cannot decrement an unsigned zero"; | |
627 | Index i; | |
628 | bool borrow = true; | |
629 | for (i = 0; borrow; i++) { | |
630 | borrow = (blk[i] == 0); | |
631 | blk[i]--; | |
632 | } | |
633 | // Zap possible leading zero (there can only be one) | |
634 | if (blk[len - 1] == 0) | |
635 | len--; | |
636 | } | |
637 | ||
638 | // Postfix decrement: same as prefix | |
639 | void BigUnsigned::operator --(int) { | |
640 | operator --(); | |
641 | } |