extrq

Extracts specified bits from the lower 64 bits of the first operand (the destination XMM register). The extracted bits are saved in the least-significant bit positions of the lower quadword of the destination; the remaining bits in the lower quadword of the destination register are cleared to 0. The upper quadword of the destination register is undefined. The portion of the source data being extracted is defined by the bit index and the field length. The bit index defines the least-significant bit of the source operand being extracted. Bits [bit index + length field – 1]:[bit index] are extracted. If the sum of the bit index + length field is greater than 64, the results are undefined. For example, if the bit index is 32 (20h) and the field length is 16 (10h), then the result in the destination register will be source [47:32] in bits 15:0, with zeros in bits 63:16. A value of zero in the field length is defined as a length of 64. If the length field is 0 and the bit index is 0, bits 63:0 of the source are extracted. For any other value of the bit index, the results are undefined. The bit index and field length can be specified as immediate values (second and first immediate operands, respectively, in the case of the three argument version of the instruction), or they can both be specified by fields in an XMM source operand. In the latter case, bits [5:0] of the XMM register specify the number of bits to extract (the field length) and bits [13:8] of the XMM register specify the index of the first bit in the field to extract. The bit index and field length are each six bits in length; other bits of the field are ignored. The diagram below illustrates the operation of this instruction. XMM1 second imm8 first imm8 127 64 63 0 7 5 0 7 5 0 shift right mask to field length XMM1 XMM2 127 64 63 0 127 13 8 5 0 shift right mask to field length