riscv-etrace 0.6.2

Decoder and tracer for RISC-V efficient instruction tracing
Documentation 
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// Copyright (C) 2025 FZI Forschungszentrum Informatik
// SPDX-License-Identifier: Apache-2.0
//! Utility for truncating fields of a specific bit-width

/// Truncate a value to a given bit-width
pub trait TruncateNum {
    /// Truncate a value to the given width `bit_count`
    ///
    /// For unsigned values, all upper bits will be zeroed. signed values will
    /// be sign-extended, preserving only the lower `bit_count` bits from the
    /// original value.
    fn truncated(self, bit_count: u8) -> Self;

    /// Retrieve the least significant byte of this value
    fn lsb(self) -> u8;
}

macro_rules! unsigned_truncate {
    ($t:ty) => {
        impl TruncateNum for $t {
            fn truncated(self, bit_count: u8) -> Self {
                self & !((!<$t>::MIN).checked_shl(bit_count.into()).unwrap_or(0))
            }

            fn lsb(self) -> u8 {
                self as u8
            }
        }
    };
}

unsigned_truncate!(u8);
unsigned_truncate!(u16);
unsigned_truncate!(u32);
unsigned_truncate!(u64);
unsigned_truncate!(usize);

impl TruncateNum for i64 {
    fn truncated(self, bit_count: u8) -> Self {
        let Some(ref_bit) = bit_count.checked_sub(1) else {
            return 0;
        };

        let upper_bits = (!0i64).checked_shl(bit_count.into()).unwrap_or(0);
        if self & (1 << ref_bit) == 0 {
            self & !upper_bits
        } else {
            self | upper_bits
        }
    }

    fn lsb(self) -> u8 {
        self as u8
    }
}