add header detector

loadsig/loadsig/src/hspice.rs

@@ -14,8 +14,12 @@ use thiserror::Error as TeError;
 pub enum Error {
     #[error("IO error {0}")]
     Io(#[from] std::io::Error),
-    #[error("fail to cast value into integral value. this usually caused by some value out of range")]
+    #[error(
+        "fail to cast value into integral value. this usually caused by some value out of range"
+    )]
     CastToInt(#[from] std::num::TryFromIntError),
+    #[error("something was overflow")]
+    Overflow,
     #[error("wrong endian integer {0:#X} in block head. it must be one of 0x4 or 0x4000000")]
     WrongEndianInt(u32),
     #[error("wrong block head value {0:#X}. it must be 0x4")]
@@ -61,7 +65,7 @@ impl HspiceBlock {
             block_len,
         }
     }
-    pub fn absolute_offset(&self, relative_offset: u32) -> u64 {
+    pub fn compute_offset(&self, relative_offset: u32) -> u64 {
         if relative_offset >= self.block_len {
             panic!("relative offset is out of range")
         } else {
@@ -156,7 +160,7 @@ where
     T: Read + Seek,
 {
     fn read(&mut self, mut buf: &mut [u8]) -> std::io::Result<usize> {
-        use std::io::{Result, Error, ErrorKind};
+        use std::io::{Error, ErrorKind, Result};
 
         let old_block_cursor = self.block_cursor;
         let old_cursor = self.cursor;
@@ -169,7 +173,10 @@ where
             }
             // Check whether we reach the tail of block chain.
             if self.block_cursor >= self.blocks.len() {
-                break Err(Error::new(ErrorKind::UnexpectedEof, "reach the tail of blocks"));
+                break Err(Error::new(
+                    ErrorKind::UnexpectedEof,
+                    "reach the tail of blocks",
+                ));
             }
             // Check whether we need to switch to next block.
             if self.cursor >= self.blocks[self.block_cursor].block_len {
@@ -182,7 +189,7 @@ where
             let remain = self.blocks[self.block_cursor].block_len - self.cursor;
             let read_count = std::cmp::min(usize::try_from(remain).unwrap(), buf.len());
             // Read data
-            let offset = self.blocks[self.block_cursor].absolute_offset(self.cursor);
+            let offset = self.blocks[self.block_cursor].compute_offset(self.cursor);
             if let Err(e) = self.reader.seek(SeekFrom::Start(offset)) {
                 break Err(e);
             }
@@ -217,34 +224,34 @@ where
         let reader_cursor = match pos {
             SeekFrom::Start(v) => {
                 if v > self.total_len {
-                    return Err(err_instance)
+                    return Err(err_instance);
                 } else {
                     v
                 }
-            },
+            }
             SeekFrom::End(v) => {
                 if v > 0 {
-                    return Err(err_instance)
+                    return Err(err_instance);
                 } else {
                     match self.total_len.checked_add_signed(v) {
                         Some(v) => v,
                         None => return Err(err_instance),
                     }
                 }
-            },
+            }
             SeekFrom::Current(v) => {
                 let current = self.offset_table[self.block_cursor] + u64::from(self.cursor);
                 match current.checked_add_signed(v) {
                     Some(v) => {
                         if v > self.total_len {
-                            return Err(err_instance)
+                            return Err(err_instance);
                         } else {
                             v
                         }
-                    },
+                    }
                     None => return Err(err_instance),
                 }
-            },
+            }
         };
 
         let block_cursor = match self.offset_table.binary_search(&reader_cursor) {
@@ -355,13 +362,34 @@ where
     }
 
     // Analyze header block count
-    // for block in &blocks {
+    let mut header_blk_cnt: Option<usize> = None;
-    //     let relative_offset = block.block_len.sa
+    for (i, block) in blocks.iter().enumerate() {
-    //     let offset = block.absolute_offset(block.block_len - (SIGNAL_NAME_LEN as u32));
+        let signal_name_len = u32::try_from(SIGNAL_NAME_LEN).unwrap();
-    // }
+        let offset = if block.block_len < signal_name_len {
+            continue;
+        } else {
+            block.compute_offset(block.block_len - signal_name_len)
+        };
+
+        reader.seek(SeekFrom::Start(offset))?;
+        let mut magic_word = [0u8; MAGIC_WORDS.len()];
+        reader.read_exact(&mut magic_word)?;
+        if &magic_word == MAGIC_WORDS {
+            match i.checked_add(1) {
+                Some(v) => header_blk_cnt = Some(v),
+                None => return Err(Error::Overflow),
+            }
+            break;
+        }
+    }
+    let header_blk_cnt = match header_blk_cnt {
+        Some(v) => v,
+        None => return Err(Error::NoMagicWords),
+    };
 
     // Build result and return.
-    Ok(HspiceBlocks::new(sim_source, blocks, 0))
+    Ok(HspiceBlocks::new(sim_source, blocks, header_blk_cnt))
 }
 
 const SIGNAL_NAME_LEN: usize = 8;
+const MAGIC_WORDS: &[u8; 4] = b"$&%#";