Module Ocaml_simd_sse.String

Refer to the Intel Intrinsics Guide (SSE4.2) for detailed specifications.
   https://www.intel.com/content/www/us/en/docs/intrinsics-guide/index.html

   String comparisons: cmp[e,i]str[m,a,c,i,o,s,z] ~a ~b

   Each intrinsic inputs two [int8x16,int16x8] vectors representing strings.
   The comparison operation is specified by a ppx_simd directive: [%bytes] for
   byte strings, and [%words] for word strings.

   ---- Lengths

   e : the lengths of the strings are given as parameters [a_len] and [b_len].
   i : the strings are assumed to be either null-terminated or full-vector-length.

   ---- Returns

   m : return a vector mask indicating which characters passed the condition.
   - With [Bit_mask]: set only the bottom [16,8] bits of the mask.
   - With [Vec_mask]: set each [byte,word] of the mask to [0xff,0xffff].

   a : return 1 if y is full-length and the comparison mask is zero
   c : return 1 if the comparison mask is non-zero
   i : return the index of the [first,last] character that passed the comparison,
   _   based on [Least_sig,Most_sig].
   o : return the least significant bit of the comparison mask
   s : return 1 if x is not full-length
   z : return 1 if y is not full-length

   ---- Examples

   Finding the index of the first byte that differs:

   [Byte.cmpistri [%bytes Signed, Eq_each, Masked_neg, Least_sig] ~a ~b]

   Creating a mask of bytes that are ASCII decimal digits:

   [
   let a = Int8x16.const 0x30 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x38 0x39 0x30 0x30 0x30 0x30 0x30 0x30 in
   Byte.cmpistrm [%bytes Signed, Eq_any, Pos, Vec_mask] ~a ~b
   ]

   Checking if any byte is not an ASCII letter:

   [
   let a = Int8x16.const 0x41 0x5A 0x61 0x7A 0x41 0x5A 0x61 0x7A 0x41 0x5A 0x61 0x7A 0x41 0x5A 0x61 0x7A in
   Byte.cmpistrc [%bytes Signed, In_range, Masked_neg] ~a ~b
   ]

   Finding the index of the first byte of the first occurance of a in b:

   [Byte.cmpistri [%bytes Signed, Eq_ordered, Pos, Least_sig] ~a ~b]