Available on

**x86 and target feature**only.`sse4a`

## Expand description

Extracts the bit range specified by `y`

from the lower 64 bits of `x`

.

The `[13:8]`

bits of `y`

specify the index of the bit-range to extract. The
`[5:0]`

bits of `y`

specify the length of the bit-range to extract. All
other bits are ignored.

If the length is zero, it is interpreted as `64`

. If the length and index
are zero, the lower 64 bits of `x`

are extracted.

If `length == 0 && index > 0`

or `length + index > 64`

the result is
undefined.