Function classify_decode

compiler/src/abi.rs:227–270

Classifies Val bits; Heap routes the host to HeapPool.

(val_bits: u64)

// Classifies Val bits; Heap routes the host to HeapPool.
pub fn classify_decode(val_bits: u64) -> DecodeBits {
    use nan_box::*;

    // Float: any non-QNAN-tagged pattern.
    if (val_bits & QNAN) != QNAN {
        return DecodeBits::Primitive {
            tag: Tag::Float as u32,
            bytes: PrimitiveBytes::Eight(f64::from_bits(val_bits).to_le_bytes()),
        };
    }
    // Int: QNAN|SIGN with payload. Sign-extend the 47-bit payload to i128 (wire width).
    if (val_bits & (QNAN | SIGN)) == TAG_INT {
        let raw = (val_bits & INT_PAYLOAD_MASK) as i64;
        let sign_extended_i64 = (raw << 16) >> 16;
        let as_i128 = sign_extended_i64 as i128;
        return DecodeBits::Primitive {
            tag: Tag::Int as u32,
            bytes: PrimitiveBytes::Sixteen(as_i128.to_le_bytes()),
        };
    }
    // Singletons and heap handles.
    let lower = val_bits & 0xF;
    if (val_bits & QNAN) == QNAN && (val_bits & SIGN) == 0 {
        if val_bits == TAG_NONE {
            return DecodeBits::Primitive {
                tag: Tag::None as u32, bytes: PrimitiveBytes::None,
            };
        }
        if val_bits == TAG_TRUE {
            return DecodeBits::Primitive {
                tag: Tag::Bool as u32, bytes: PrimitiveBytes::Bool(1),
            };
        }
        if val_bits == TAG_FALSE {
            return DecodeBits::Primitive {
                tag: Tag::Bool as u32, bytes: PrimitiveBytes::Bool(0),
            };
        }
        if lower >= 4 {
            return DecodeBits::Heap;
        }
    }
    DecodeBits::Invalid
}