Per prima cosa il moltplicatore e' impostato come una potenza di due (nell'esempio come 2^7)
Cio' permette di evitare il piu' possibile moltiplicazioni e divisioni che possono essere sostituite da shift a destra per la divisione e shift a sinistra per la moltiplicazione (tipicamente per moltiplicare e dividere un numero per due e' sufficiente effettuare lo shift dei bit di una posizione)
Un altro trucco e' quello di utilizzare una tabella precalcolata dei quadrati dei primi 700 numeri.
Per la matrice deve essere gestita anche la possibilita' dei quadranti negativi... per simulare il comando abs di C e' stato usato il bit shit con la seguente formula
int x_abs = (x^(x>>31))-(x>>31);
---------------------------------------------------------------------
#include <SDL/SDL.h>
#include <math.h>
#define SCREEN_WIDTH 159
#define SCREEN_HEIGHT 99
#define SCREEN_DEPTH 8
unsigned char iterazioni = 15; //byte
unsigned char keypress = 0; //byte
unsigned char k; //byte
short int a,b,nx,ny; // dimensione word 16 bit
int t,limite,x,y; // 32 bit
unsigned short int i,j,de,di; // dimensione word 16 bit
unsigned int inizio,fine = 0;
int main ()
{
SDL_Surface *screen;
Uint8 *p;
SDL_Init(SDL_INIT_VIDEO);
screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_DEPTH, SDL_SWSURFACE);
//-------------------------------------------------------
unsigned int square[]={
0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100,
121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441,
484, 529, 576, 625, 676, 729, 784, 841, 900, 961, 1024,
1089, 1156, 1225, 1296, 1369, 1444, 1521, 1600, 1681, 1764, 1849,
1936, 2025, 2116, 2209, 2304, 2401, 2500, 2601, 2704, 2809, 2916,
3025, 3136, 3249, 3364, 3481, 3600, 3721, 3844, 3969, 4096, 4225,
4356, 4489, 4624, 4761, 4900, 5041, 5184, 5329, 5476, 5625, 5776,
5929, 6084, 6241, 6400, 6561, 6724, 6889, 7056, 7225, 7396, 7569,
7744, 7921, 8100, 8281, 8464, 8649, 8836, 9025, 9216, 9409, 9604,
9801, 10000, 10201, 10404, 10609, 10816, 11025, 11236, 11449, 11664, 11881,
12100, 12321, 12544, 12769, 12996, 13225, 13456, 13689, 13924, 14161, 14400,
14641, 14884, 15129, 15376, 15625, 15876, 16129, 16384, 16641, 16900, 17161,
17424, 17689, 17956, 18225, 18496, 18769, 19044, 19321, 19600, 19881, 20164,
20449, 20736, 21025, 21316, 21609, 21904, 22201, 22500, 22801, 23104, 23409,
23716, 24025, 24336, 24649, 24964, 25281, 25600, 25921, 26244, 26569, 26896,
27225, 27556, 27889, 28224, 28561, 28900, 29241, 29584, 29929, 30276, 30625,
30976, 31329, 31684, 32041, 32400, 32761, 33124, 33489, 33856, 34225, 34596,
34969, 35344, 35721, 36100, 36481, 36864, 37249, 37636, 38025, 38416, 38809,
39204, 39601, 40000, 40401, 40804, 41209, 41616, 42025, 42436, 42849, 43264,
43681, 44100, 44521, 44944, 45369, 45796, 46225, 46656, 47089, 47524, 47961,
48400, 48841, 49284, 49729, 50176, 50625, 51076, 51529, 51984, 52441, 52900,
53361, 53824, 54289, 54756, 55225, 55696, 56169, 56644, 57121, 57600, 58081,
58564, 59049, 59536, 60025, 60516, 61009, 61504, 62001, 62500, 63001, 63504,
64009, 64516, 65025, 65536, 66049, 66564, 67081, 67600, 68121, 68644, 69169,
69696, 70225, 70756, 71289, 71824, 72361, 72900, 73441, 73984, 74529, 75076,
75625, 76176, 76729, 77284, 77841, 78400, 78961, 79524, 80089, 80656, 81225,
81796, 82369, 82944, 83521, 84100, 84681, 85264, 85849, 86436, 87025, 87616,
88209, 88804, 89401, 90000, 90601, 91204, 91809, 92416, 93025, 93636, 94249,
94864, 95481, 96100, 96721, 97344, 97969, 98596, 99225, 99856, 100489, 101124,
101761, 102400, 103041, 103684, 104329, 104976, 105625, 106276, 106929, 107584, 108241,
108900, 109561, 110224, 110889, 111556, 112225, 112896, 113569, 114244, 114921, 115600,
116281, 116964, 117649, 118336, 119025, 119716, 120409, 121104, 121801, 122500, 123201,
123904, 124609, 125316, 126025, 126736, 127449, 128164, 128881, 129600, 130321, 131044,
131769, 132496, 133225, 133956, 134689, 135424, 136161, 136900, 137641, 138384, 139129,
139876, 140625, 141376, 142129, 142884, 143641, 144400, 145161, 145924, 146689, 147456,
148225, 148996, 149769, 150544, 151321, 152100, 152881, 153664, 154449, 155236, 156025,
156816, 157609, 158404, 159201, 160000, 160801, 161604, 162409, 163216, 164025, 164836,
165649, 166464, 167281, 168100, 168921, 169744, 170569, 171396, 172225, 173056, 173889,
174724, 175561, 176400, 177241, 178084, 178929, 179776, 180625, 181476, 182329, 183184,
184041, 184900, 185761, 186624, 187489, 188356, 189225, 190096, 190969, 191844, 192721,
193600, 194481, 195364, 196249, 197136, 198025, 198916, 199809, 200704, 201601, 202500,
203401, 204304, 205209, 206116, 207025, 207936, 208849, 209764, 210681, 211600, 212521,
213444, 214369, 215296, 216225, 217156, 218089, 219024, 219961, 220900, 221841, 222784,
223729, 224676, 225625, 226576, 227529, 228484, 229441, 230400, 231361, 232324, 233289,
234256, 235225, 236196, 237169, 238144, 239121, 240100, 241081, 242064, 243049, 244036,
245025, 246016, 247009, 248004, 249001, 250000, 251001, 252004, 253009, 254016, 255025,
256036, 257049, 258064, 259081, 260100, 261121, 262144, 263169, 264196, 265225, 266256,
267289, 268324, 269361, 270400, 271441, 272484, 273529, 274576, 275625, 276676, 277729,
278784, 279841, 280900, 281961, 283024, 284089, 285156, 286225, 287296, 288369, 289444,
290521, 291600, 292681, 293764, 294849, 295936, 297025, 298116, 299209, 300304, 301401,
302500, 303601, 304704, 305809, 306916, 308025, 309136, 310249, 311364, 312481, 313600,
314721, 315844, 316969, 318096, 319225, 320356, 321489, 322624, 323761, 324900, 326041,
327184, 328329, 329476, 330625, 331776, 332929, 334084, 335241, 336400, 337561, 338724,
339889, 341056, 342225, 343396, 344569, 345744, 346921, 348100, 349281, 350464, 351649,
352836, 354025, 355216, 356409, 357604, 358801, 360000, 361201, 362404, 363609, 364816,
366025, 367236, 368449, 369664, 370881, 372100, 373321, 374544, 375769, 376996, 378225,
379456, 380689, 381924, 383161, 384400, 385641, 386884, 388129, 389376, 390625, 391876,
393129, 394384, 395641, 396900, 398161, 399424, 400689, 401956, 403225, 404496, 405769,
407044, 408321, 409600, 410881, 412164, 413449, 414736, 416025, 417316, 418609, 419904,
421201, 422500, 423801, 425104, 426409, 427716, 429025, 430336, 431649, 432964, 434281,
435600, 436921, 438244, 439569, 440896, 442225, 443556, 444889, 446224, 447561, 448900,
450241, 451584, 452929, 454276, 455625, 456976, 458329, 459684, 461041, 462400, 463761,
465124, 466489, 467856, 469225, 470596, 471969, 473344, 474721, 476100, 477481, 478864,
480249, 481636, 483025, 484416, 485809, 487204, 488601, 490000, 491401, 492804, 494209,
495616, 497025, 498436, 499849, 501264, 502681, 504100, 505521, 506944, 508369, 509796,
511225, 512656, 514089, 515524, 516961, 518400, 519841, 521284, 522729, 524176, 525625,
527076, 528529, 529984, 531441, 532900, 534361, 535824, 537289, 538756, 540225, 541696,
543169, 544644, 546121, 547600, 549081, 550564, 552049, 553536, 555025, 556516, 558009,
559504, 561001, 562500, 564001, 565504, 567009, 568516, 570025, 571536, 573049, 574564
};
inizio = SDL_GetTicks();
int bit = 7;
a = -2<<bit;
de = 2;
di = 3;
limite = 1<<(bit+2);
for (i=0;i<SCREEN_WIDTH;i++)
{
a=a+de;
b=-154;
for (j=0;j<SCREEN_HEIGHT;j++)
{
b=b+di;
x=0;
y=0;
for (k=1;k<iterazioni;k++)
{
int x_abs = (x^(x>>31))-(x>>31);
int y_abs = (y^(y>>31))-(y>>31);
nx = (square[x_abs]>>bit) - (square[y_abs]>>bit) + a;
y = ((x*y)>>(bit-1))+b;
int nx_abs = (nx^(nx>>31))-(nx>>31);
y_abs = (y^(y>>31))-(y>>31);
t = (square[nx_abs]>>bit) + (square[y_abs]>>bit);
//t = (square[abs(nx)]>>bit) + (square[abs(y)]>>bit);
//t = (nx*nx>>bit) + (y*y>>bit);
if (t>limite)
{
//plot
p = (Uint8 *)screen->pixels + j * screen->pitch + i * screen->format->BytesPerPixel;
*p=255;
k =26;
}
x=nx;
}
}
}
SDL_Flip(screen);
fine = SDL_GetTicks();
printf("Esecuzione 5: %d\n", fine-inizio);
bool done=false;
while (!done)
{
// message processing loop
SDL_Event event;
while (SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_QUIT:
done = true;
break;
case SDL_KEYDOWN:
{
// exit if ESCAPE is pressed
if (event.key.keysym.sym == SDLK_ESCAPE)
done = true;
break;
}
} // end switch
} // end of message proc
}
//---------------------------------------------
SDL_Quit();
return(0);
}
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