Function s_imm

crates/virtual-machine/src/cpu/decoder.rs:907–911

S-type immediate: bits[31:25] || bits[11:7], sign-extended to 12 bits.

(word: u32)

    let bit11 = field(word, 7, 7) << 11;
    let bits10_5 = field(word, 30, 25) << 5;
    let bits4_1 = field(word, 11, 8) << 1;
    sign_ext(bit12 | bit11 | bits10_5 | bits4_1, 13)
}

// J-type immediate: [31]<<20 | [19:12]<<12 | [20]<<11 | [30:21]<<1, sign-extended to 21 bits.
fn j_imm(word: u32) -> i64 {
    let bit20 = field(word, 31, 31) << 20;
    let bits19_12 = field(word, 19, 12) << 12;