pto.vcls

pto.vcls is part of the Unary Vector Instructions instruction set.

Summary

%result holds the leading-sign-bit count per active lane.

Mechanism

pto.vcls computes the lane-wise count of leading sign bits: dst[i] = count_leading_sign_bits(src[i]). This counts the number of identical bits (sign bit) starting from the most significant bit until the first opposite bit is found. Integer element types only. Inactive lanes leave the destination unchanged.

Syntax

PTO Assembly Form

vcls %result, %input, %mask

AS Level 1 (SSA)

%result = pto.vcls %input, %mask : !pto.vreg<NxT>, !pto.mask<G> -> !pto.vreg<NxT>

Documented A5 types or forms: all integer types.

Inputs

Operand Type Description
%input !pto.vreg<NxT> Source vector register; read at each active lane i
%mask !pto.mask<G> Predicate mask; lanes where mask bit is 1 (true) are active

Expected Outputs

Result Type Description
%result !pto.vreg<NxT> Lane-wise leading-sign-bit count: dst[i] = count_leading_sign_bits(src[i]) on active lanes; inactive lanes are unmodified

Side Effects

This operation has no architectural side effect beyond producing its SSA results. It does not implicitly reserve buffers, signal events, or establish memory fences unless the form says so.

Constraints

Constraints

Integer element types only. This operation is sign-aware, so signed interpretation matters.

Exceptions

Exceptions

  • The verifier rejects illegal operand shapes, unsupported element types, and attribute combinations that are not valid for the selected instruction set or target profile.
  • Any additional illegality stated in the constraints section is also part of the contract.

Target-Profile Restrictions

Target-Profile Restrictions
  • Documented A5 coverage: all integer types.
  • A5 is the most detailed concrete profile in the current manual; CPU simulation and A2/A3-class targets may support narrower subsets or emulate the behavior while preserving the visible PTO contract.
  • Code that depends on an instruction-set-specific type list, distribution mode, or fused form should treat that dependency as target-profile-specific unless the PTO manual states cross-target portability explicitly.

Examples

for (int i = 0; i < N; i++)
    dst[i] = count_leading_sign_bits(src[i]);