decouple magic number from current lib; tag 0.1.0-a4

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "dual_balanced_ternary"
-version = "0.1.0-a3"
+version = "0.1.0-a4"
 edition = "2018"
 license = "MIT"
 description = "Dual Balanced Ternary Arithmetic"

README.md

@@ -20,7 +20,7 @@ cargo run --example buffer
 Notice, current buffer format is not compact, but conceptually:
 
 ```text
-[magic 3]+[integral length]+[integral pairs]+[fractional pairs]
+[integral length]+[integral pairs]+[fractional pairs]
 ```
 
 since a dbt digits pair takes `81` and `u8` takes `256`, `2/3` of spaces are wasted.

examples/buffer.rs

@@ -4,8 +4,8 @@ pub fn main() -> Result<(), String> {
   println!("{:?}", ternary("&1.1").to_buffer());
   println!("{:?}", ternary("&14.14").to_buffer());
 
-  println!("{:?}", DualBalancedTernary::from_buffer(vec![3, 1, 21, 21]));
-  println!("{:?}", DualBalancedTernary::from_buffer(vec![3, 1, 65, 20]));
+  println!("{:?}", DualBalancedTernary::from_buffer(vec![1, 21, 21]));
+  println!("{:?}", DualBalancedTernary::from_buffer(vec![1, 65, 20]));
 
   println!("TODO {:?}", ternary("&12.12").to_buffer()?);
 

src/primes.rs

@@ -390,11 +390,11 @@ impl DualBalancedTernary {
   }
 
   /// buffer format
-  /// [magic 3]+[integral length]+[integral pairs]+[fractional pairs]
+  /// [integral length]+[integral pairs]+[fractional pairs]
   pub fn to_buffer(&self) -> Result<Vec<u8>, String> {
     let int_len = self.integral.len();
     if int_len < 256 {
-      let mut buf: Vec<u8> = vec![3, int_len as u8];
+      let mut buf: Vec<u8> = vec![int_len as u8];
       // for integral part, put space 5 at head
       let mut halfed = false;
       let mut prev: u8 = 0;
@@ -415,7 +415,7 @@ impl DualBalancedTernary {
       }
 
       // expected handled by pair
-      assert_eq!(buf.len(), ((int_len + 1) >> 1) + 2);
+      assert_eq!(buf.len(), ((int_len + 1) >> 1) + 1);
 
       // for integral part, put space 5 at tail
       for x in &self.fractional {
@@ -440,30 +440,27 @@ impl DualBalancedTernary {
   }
 
   /// buffer format
-  /// [magic 3]+[integral length]+[integral pairs]+[fractional pairs]
+  /// [integral length]+[integral pairs]+[fractional pairs]
   pub fn from_buffer(buf: Vec<u8>) -> Result<Self, String> {
-    if buf.len() < 2 {
+    if buf.is_empty() {
       return Err(String::from("dbt buffer expected >=2 u8 numbers"));
     }
-    if buf[0] != 3 {
-      return Err(String::from("dbt magic number should be 3"));
-    }
 
-    let int_range = (buf[1] + 1) as usize >> 1;
+    let int_range = (buf[0] + 1) as usize >> 1;
 
-    if buf.len() < (int_range + 2) {
+    if buf.len() < (int_range + 1) {
       return Err(String::from("dbt buffer length smaller than integral size"));
     }
     let mut integral: Vec<DualBalancedTernaryDigit> = vec![];
     let mut fractional: Vec<DualBalancedTernaryDigit> = vec![];
 
     // println!("buffer: {:?}", buf);
     for (idx, x) in buf.iter().enumerate() {
-      if idx < 2 {
+      if idx < 1 {
         continue;
       }
       // println!("reading: {} {}", idx, x);
-      if idx < (int_range + 2) as usize {
+      if idx < (int_range + 1) as usize {
         integral.push(DualBalancedTernaryDigit::from_u8((x & 0b11110000) >> 4)?);
         integral.push(DualBalancedTernaryDigit::from_u8(x & 0b00001111)?);
       } else {