# Function sm3p1

Source

    pub fn sm3p1(rs1: u32) -> u32

🔬This is a nightly-only experimental API. (`riscv_ext_intrinsics` #114544)
Available on RISC-V RV64 and target feature `zksh` only.
Expand description

Implements the P1 transformation function as used in the SM3 hash function [4, 30].

This instruction is supported for the RV32 and RV64 base architectures. It implements the P1 transform of the SM3 hash function [4, 30]. This instruction must always be implemented such that its execution latency does not depend on the data being operated on.

Source: RISC-V Cryptography Extensions Volume I: Scalar & Entropy Source Instructions

Version: v1.0.1

Section: 3.42

## §Details

`P1` transformation function as is used in the SM3 hash algorithm

This function is included in `Zksh` extension. It’s defined as:

    P1(X) = X ⊕ (X ≪ 15) ⊕ (X ≪ 23)

where `⊕` represents 32-bit xor, and `≪ k` represents rotate left by `k` bits.

In the SM3 algorithm, the `P1` transformation is used to expand message, where expanded word `Wj` can be generated from the previous words. The whole process can be described as the following pseudocode:

    FOR j=16 TO 67
        Wj ← P1(Wj−16 ⊕ Wj−9 ⊕ (Wj−3 ≪ 15)) ⊕ (Wj−13 ≪ 7) ⊕ Wj−6
    ENDFOR