t Length Strings, Return Index</h1>

<table>
<tr>
<th>Opcode/Instruction</th>
<th>Op/En</th>
<th>64/32 bit Mode Support</th>
<th>CPUID Feature Flag</th>
<th>Description</th></tr>
<tr>
<td>66 0F 3A 63 <em>/r imm8</em> PCMPISTRI <em>xmm1, xmm2/m128, imm8</em></td>
<td>RM</td>
<td>V/V</td>
<td>SSE4_2</td>
<td>Perform a packed comparison of string data with implicit lengths, generating an index, and storing the result in ECX.</td></tr>
<tr>
<td>VEX.128.66.0F3A.WIG 63 /r ib VPCMPISTRI <em>xmm1, xmm2/m128, imm8</