| 287 | #pragma warning(disable : 4035) // Disable warning "no return value" |
| 288 | #endif |
| 289 | AGG_INLINE unsigned fast_sqrt(unsigned val) |
| 290 | { |
| 291 | #if defined(_M_IX86) && defined(_MSC_VER) && !defined(AGG_NO_ASM) |
| 292 | // For Ix86 family processors this assembler code is used. |
| 293 | // The key command here is bsr - determination the number of the most |
| 294 | // significant bit of the value. For other processors |
| 295 | //(and maybe compilers) the pure C "#else" section is used. |
| 296 | __asm |
| 297 | { |
| 298 | mov ebx, val |
| 299 | mov edx, 11 |
| 300 | bsr ecx, ebx |
| 301 | sub ecx, 9 |
| 302 | jle less_than_9_bits |
| 303 | shr ecx, 1 |
| 304 | adc ecx, 0 |
| 305 | sub edx, ecx |
| 306 | shl ecx, 1 |
| 307 | shr ebx, cl |
| 308 | less_than_9_bits: |
| 309 | xor eax, eax |
| 310 | mov ax, g_sqrt_table[ebx*2] |
| 311 | mov ecx, edx |
| 312 | shr eax, cl |
| 313 | } |
| 314 | #else |
| 315 | |
| 316 | // This code is actually pure C and portable to most |
| 317 | // arcitectures including 64bit ones. |
| 318 | unsigned t = val; |
| 319 | int bit = 0; |
| 320 | unsigned shift = 11; |
| 321 | |
| 322 | // The following piece of code is just an emulation of the |
| 323 | // Ix86 assembler command "bsr" (see above). However on old |
| 324 | // Intels (like Intel MMX 233MHz) this code is about twice |
| 325 | // faster (sic!) then just one "bsr". On PIII and PIV the |
| 326 | // bsr is optimized quite well. |
| 327 | bit = t >> 24; |
| 328 | if (bit) |
| 329 | { |
| 330 | bit = g_elder_bit_table[bit] + 24; |
| 331 | } |
| 332 | else |
| 333 | { |
| 334 | bit = (t >> 16) & 0xFF; |
| 335 | if (bit) |
| 336 | { |
| 337 | bit = g_elder_bit_table[bit] + 16; |
| 338 | } |
| 339 | else |
| 340 | { |
| 341 | bit = (t >> 8) & 0xFF; |
| 342 | if (bit) |
| 343 | { |
| 344 | bit = g_elder_bit_table[bit] + 8; |
| 345 | } |
| 346 | else |
no outgoing calls
no test coverage detected