don't use casts like that

src/durandal/bin.rs

@@ -4,14 +4,14 @@ use crate::durandal::err::*;
 use serde::Serialize;
 use std::{fmt, num::NonZeroU16, slice::SliceIndex};
 
-/// Returns a byte array from `b` at `i`.
+/// Returns a `[u8]` from `b` at `i`.
 pub fn c_data<I>(b: &[u8], i: I) -> ResultS<&<I as SliceIndex<[u8]>>::Output>
    where I: SliceIndex<[u8]>
 {
    ok!(b.get(i), "not enough data")
 }
 
-/// Returns a byte from `b` at `i`.
+/// Returns a `u8` from `b` at `i`.
 pub fn c_byte(b: &[u8], i: usize) -> ResultS<u8>
 {
    match b.get(i) {
@@ -70,6 +70,16 @@ pub fn o_u32b(b: &[u8], i: usize) -> Option<u32>
    }
 }
 
+/// Returns a big-endian `i32` from `b` at `i`.
+pub fn o_i32b(b: &[u8], i: usize) -> Option<i32>
+{
+   if i + 3 < b.len() {
+      Some(i32::from_be_bytes([b[i], b[i + 1], b[i + 2], b[i + 3]]))
+   } else {
+      None
+   }
+}
+
 /// Returns a big-endian `u16` from `b` at `i`.
 pub fn o_u16b(b: &[u8], i: usize) -> Option<u16>
 {
@@ -80,12 +90,13 @@ pub fn o_u16b(b: &[u8], i: usize) -> Option<u16>
    }
 }
 
-/// Returns a big-endian `i32` from `b` at `i`.
-pub fn o_i32b(b: &[u8], i: usize) -> Option<i32>
+/// Returns a big-endian `i16` from `b` at `i`.
+pub fn o_i16b(b: &[u8], i: usize) -> Option<i16>
 {
-   match o_u32b(b, i) {
-      Some(n) => Some(n as i32),
-      None => None,
+   if i + 1 < b.len() {
+      Some(i16::from_be_bytes([b[i], b[i + 1]]))
+   } else {
+      None
    }
 }
 
@@ -124,7 +135,7 @@ impl ObjID
    {
       match self.0 {
          None => None,
-         Some(n) => Some(n.get()),
+         Some(n) => Some(n.get() - 1),
       }
    }
 }