add merge_unbias

src/lib.rs

@@ -38,6 +38,23 @@ impl F8 {
 		assert!(e <= E_STORAGE_MAX);
 		Self((e << M_BITS) | m)
 	}
+
+	fn merge_unbias(in_m: u8, in_e: i8) -> Self {
+		if in_m == 0 {
+			return Self(0);
+		}
+		let base_e = in_m.ilog2() as u8;
+		let off = base_e as i8 - M_BITS as i8;
+		let m = if off >= 0 { in_m >> off } else { in_m << -off };
+		let e = (base_e as i8) + in_e + (E_BIAS as i8);
+		if e < 0 {
+			return Self(0);
+		}
+		if e > E_STORAGE_MAX as i8 {
+			return Self(0xff);
+		}
+		Self::merge(m & M_STORAGE_MAX, e as u8)
+	}
 }
 
 impl std::fmt::Binary for F8 {
@@ -134,6 +151,21 @@ mod tests {
 		}
 	}
 
+	#[test]
+	fn test_merge() {
+		assert_eq!(f32::from(F8::merge_unbias(0, 0)), 0.0);
+		assert_eq!(f32::from(F8::merge_unbias(1, 0)), 1.0);
+		assert_eq!(f32::from(F8::merge_unbias(1, 1)), 2.0);
+		assert_eq!(f32::from(F8::merge_unbias(1, -1)), 0.5);
+		assert_eq!(f32::from(F8::merge_unbias(3, 0)), 3.0);
+		assert_eq!(f32::from(F8::merge_unbias(3, 1)), 6.0);
+		assert_eq!(f32::from(F8::merge_unbias(3, -1)), 1.5);
+		assert_eq!(
+			f32::from(F8::merge_unbias(EXACT_INT_MAX, 0)),
+			EXACT_INT_MAX as f32
+		);
+	}
+
 	#[test]
 	fn test_display() {
 		fn fmt_split(m: u8, e: u8) -> String {