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| <title>POPCNT — Return the Count of Number of Bits Set to 1 </title></head> |
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| <h1>POPCNT — Return the Count of Number of Bits Set to 1</h1> |
| <table> |
| <tr> |
| <th>Opcode</th> |
| <th>Instruction</th> |
| <th>Op/En</th> |
| <th>64-Bit Mode</th> |
| <th>Compat/Leg Mode</th> |
| <th>Description</th></tr> |
| <tr> |
| <td>F3 0F B8 /r</td> |
| <td>POPCNT <em>r16, r/m16</em></td> |
| <td>RM</td> |
| <td>Valid</td> |
| <td>Valid</td> |
| <td>POPCNT on <em>r/m16</em></td></tr> |
| <tr> |
| <td>F3 0F B8 /r</td> |
| <td>POPCNT <em>r32, r/m32</em></td> |
| <td>RM</td> |
| <td>Valid</td> |
| <td>Valid</td> |
| <td>POPCNT on <em>r/m32</em></td></tr> |
| <tr> |
| <td>F3 REX.W 0F B8 <em>/r</em></td> |
| <td>POPCNT <em>r64, r/m64</em></td> |
| <td>RM</td> |
| <td>Valid</td> |
| <td>N.E.</td> |
| <td>POPCNT on <em>r/m64</em></td></tr></table> |
| <h3>Instruction Operand Encoding</h3> |
| <table> |
| <tr> |
| <td>Op/En</td> |
| <td>Operand 1</td> |
| <td>Operand 2</td> |
| <td>Operand 3</td> |
| <td>Operand 4</td></tr> |
| <tr> |
| <td>RM</td> |
| <td>ModRM:reg (w)</td> |
| <td>ModRM:r/m (r)</td> |
| <td>NA</td> |
| <td>NA</td></tr></table> |
| <h2>Description</h2> |
| <p>This instruction calculates of number of bits set to 1 in the second operand (source) and returns the count in the first operand (a destination register).</p> |
| <h2>Operation</h2> |
| <pre>Count = 0; |
| For (i=0; i < OperandSize; i++) |
| { |
| IF (SRC[ i] = 1) // i’th bit |
| THEN Count++; FI; |
| } |
| DEST ← Count;</pre> |
| <h2>Flags Affected</h2> |
| <p>OF, SF, ZF, AF, CF, PF are all cleared. ZF is set if SRC = 0, otherwise ZF is cleared.</p> |
| <h2>Intel C/C++ Compiler Intrinsic Equivalent</h2> |
| <p>POPCNT:</p> |
| <p> int _mm_popcnt_u32(unsigned int a);</p> |
| <p>POPCNT:</p> |
| <p> int64_t _mm_popcnt_u64(unsigned __int64 a);</p> |
| <h2>Protected Mode Exceptions</h2> |
| <table class="exception-table"> |
| <tr> |
| <td>#GP(0)</td> |
| <td>If a memory operand effective address is outside the CS, DS, ES, FS or GS segments.</td></tr> |
| <tr> |
| <td>#SS(0)</td> |
| <td>If a memory operand effective address is outside the SS segment limit.</td></tr> |
| <tr> |
| <td>#PF (fault-code)</td> |
| <td>For a page fault.</td></tr> |
| <tr> |
| <td>#AC(0)</td> |
| <td>If an unaligned memory reference is made while the current privilege level is 3 and alignment checking is enabled.</td></tr> |
| <tr> |
| <td>#UD</td> |
| <td> |
| <p>If CPUID.01H:ECX.POPCNT [Bit 23] = 0.</p> |
| <p>If LOCK prefix is used.</p></td></tr></table> |
| <h2>Real-Address Mode Exceptions</h2> |
| <table class="exception-table"> |
| <tr> |
| <td>#GP(0)</td> |
| <td>If any part of the operand lies outside of the effective address space from 0 to 0FFFFH.</td></tr> |
| <tr> |
| <td>#SS(0)</td> |
| <td>If a memory operand effective address is outside the SS segment limit.</td></tr> |
| <tr> |
| <td>#UD</td> |
| <td> |
| <p>If CPUID.01H:ECX.POPCNT [Bit 23] = 0.</p> |
| <p>If LOCK prefix is used.</p></td></tr></table> |
| <h2>Virtual 8086 Mode Exceptions</h2> |
| <table class="exception-table"> |
| <tr> |
| <td>#GP(0)</td> |
| <td>If any part of the operand lies outside of the effective address space from 0 to 0FFFFH.</td></tr> |
| <tr> |
| <td>#SS(0)</td> |
| <td>If a memory operand effective address is outside the SS segment limit.</td></tr> |
| <tr> |
| <td>#PF (fault-code)</td> |
| <td>For a page fault.</td></tr> |
| <tr> |
| <td>#AC(0)</td> |
| <td>If an unaligned memory reference is made while alignment checking is enabled.</td></tr> |
| <tr> |
| <td>#UD</td> |
| <td> |
| <p>If CPUID.01H:ECX.POPCNT [Bit 23] = 0.</p> |
| <p>If LOCK prefix is used.</p></td></tr></table> |
| <h2>Compatibility Mode Exceptions</h2> |
| <p>Same exceptions as in Protected Mode.</p> |
| <h2>64-Bit Mode Exceptions</h2> |
| <table class="exception-table"> |
| <tr> |
| <td>#GP(0)</td> |
| <td>If the memory address is in a non-canonical form.</td></tr> |
| <tr> |
| <td>#SS(0)</td> |
| <td>If a memory address referencing the SS segment is in a non-canonical form.</td></tr> |
| <tr> |
| <td>#PF (fault-code)</td> |
| <td>For a page fault.</td></tr> |
| <tr> |
| <td>#AC(0)</td> |
| <td>If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.</td></tr> |
| <tr> |
| <td>#UD</td> |
| <td> |
| <p>If CPUID.01H:ECX.POPCNT [Bit 23] = 0.</p> |
| <p>If LOCK prefix is used.</p></td></tr></table></body></html> |