remove unused function lt_field_8_bit

Author: jialinli98

README.md

@@ -142,6 +142,43 @@ The parser uses several lookup tables generated from `src/_table_generation/`:
 - `JSON_CAPTURE_TABLE`: Character-by-character parsing rules
 - `TOKEN_VALIDATION_TABLE`: JSON grammar validation
 
+### Example walkthrough
+We can take a look at raw Json text {"name": "Alice", "age": 30} and how it is being parsed.
+First, The parser reads the JSON one character at a time and uses lookup tables to decide what to do with each character. For {"name": "Alice"}, 
+Character: {  → "Start scanning an object (grammar_capture)"
+Character: "  → "Start scanning a string" 
+Character: n  → "Continue scanning the string"
+Character: a  → "Continue scanning the string"
+Character: m  → "Continue scanning the string"
+Character: e  → "Continue scanning the string"
+Character: "  → "End the string"
+Character: :  → "Key-value separator"
+Character: "  → "Start scanning a string"
+Character: A  → "Continue scanning the string"
+Character: l  → "Continue scanning the string"
+Character: i  → "Continue scanning the string"
+Character: c  → "Continue scanning the string"
+Character: e  → "Continue scanning the string"
+Character: "  → "End the string"
+Character: }  → "End the object"
+
+The parser builds a list of "tokens", the basic building blocks of the JSON, which becomes
+1. BEGIN_OBJECT_TOKEN ({)
+2. STRING_TOKEN ("name")
+3. KEY_SEPARATOR_TOKEN (:)
+4. STRING_TOKEN ("Alice")
+5. END_OBJECT_TOKEN (})
+
+The parser converts tokens into structured entries with parent-child relationships.
+Each entry knows:
+What type it is (object, string, number, etc.)
+Who its parent is
+How many children it has
+Where it is in the original JSON
+
+Finally, the parser sorts entries by their key hashes for fast lookups.
+Original order: [{"name": "Alice"}, {"age": 30}]
+Sorted order:   [{"age": 30}, {"name": "Alice"}]
 
 # Acknowledgements
 

src/_comparison_tools/lt.nr

@@ -54,18 +54,6 @@ pub fn lt_field_16_bit(x: Field, y: Field) -> bool {
     predicate
 }
 
-pub fn lt_field_8_bit(x: Field, y: Field) -> bool {
-    // Safety: check the comments below
-    let predicate = unsafe { get_lt_predicate_f(x, y) };
-    let delta = y as Field - x as Field;
-    let lt_parameter = 2 * (predicate as Field) * delta - predicate as Field - delta;
-    // checks that the bit length of lt_parameter is 8
-    // i.e. checks the sign of lt_parameter
-    lt_parameter.assert_max_bit_size::<8>();
-
-    predicate
-}
-
 pub fn assert_gt_240_bit(lhs: Field, rhs: Field) {
     // lhs > rhs
     // -> lhs - rhs > 0

src/_table_generation/table_generation.md

@@ -66,4 +66,6 @@ LITERAL_CAPTURE_INCREASE_LENGTH: True for t,r,u,e,f,a,l,s,n
 GRAMMAR_CAPTURE_ERROR_FLAG
 STRING_CAPTURE_ERROR_FLAG
 NUMERIC_CAPTURE_ERROR_FLAG
-LITERAL_CAPTURE_ERROR_FLAG
+LITERAL_CAPTURE_ERROR_FLAG
+
+PROCESS_RAW_TRANSCRIPT_TABLE: This table is used to post-process the raw transcript and add missing grammar tokens that were not captured during the initial scanning in build_transcript. Input: encoded_ascii of the last token in each entry (scan_mode + ascii character). Output: containing: token: The token type for this entry, new_grammar: Whether to add a missing grammar token, and scan_token: The type of grammar token to add (if needed), such as END_OBJECT_TOKEN }, or VALUE_SEPARATOR_TOKEN comma.

src/json.nr

@@ -540,30 +540,36 @@ impl<let NumBytes: u32, let NumPackedFields: u32, let MaxNumTokens: u32, let Max
     unconstrained fn __build_transcript(self) -> [Field; MaxNumTokens] {
         let mut raw_transcript: [Field; MaxNumTokens] = [0; MaxNumTokens];
         let mut transcript_ptr: u32 = 0;
+        // We start in grammar capture mode, expecting to see a { or [.
         let mut scan_mode = GRAMMAR_CAPTURE;
         let mut length: Field = 0;
         let mut previous_was_potential_escape_sequence = 0;
         for i in 0..NumBytes {
-            // while this assert is in an unconstrained function, the out of bounds accesss `raw_transcript[transcript_ptr]` in build_transcript also generates failing constraints
+            // while this assert is in an unconstrained function, the out of bounds access `raw_transcript[transcript_ptr]` in build_transcript also generates failing constraints
             assert(transcript_ptr < MaxNumTokens, "build_transcript: MaxNumTokens limit exceeded!");
             let ascii = self.json[i];
 
             let encoded_ascii =
                 previous_was_potential_escape_sequence * 1024 + scan_mode * 256 + ascii as Field;
             let ScanData { scan_token, push_transcript, increase_length, is_potential_escape_sequence } =
                 ScanData::from_field(JSON_CAPTURE_TABLE[cast_num_to_u32(encoded_ascii)]);
+            // increase_length and push_transcript are contradictory
+            // increase_length = true means "extend the current token"
+            // push_transcript = true means "start a new token"
             let mut push_transcript = push_transcript;
             let mut scan_token = scan_token;
             let mut increase_length = increase_length;
 
             if push_transcript == 1 {
                 let new_entry = RawTranscriptEntry::to_field(
+                    // index is where the token starts in the original JSON
                     RawTranscriptEntry { encoded_ascii, index: i as Field - length, length },
                 );
 
                 raw_transcript[transcript_ptr] = new_entry;
                 transcript_ptr += 1;
-                length = increase_length;
+                // reset length to 0 as we're starting a new token
+                length = 0;
             } else {
                 length += increase_length;
             }
@@ -616,7 +622,8 @@ impl<let NumBytes: u32, let NumPackedFields: u32, let MaxNumTokens: u32, let Max
 
         // Safety: check the comments below
         let raw_transcript = unsafe { self.__build_transcript() };
-
+        
+        // steps to verify the transcript is correct
         // 14 gates per iteration, plus fixed cost for initing 2,048 size lookup table (4,096 gates)
         let mut previous_was_potential_escape_sequence = 0;
         for i in 0..NumBytes {
@@ -659,10 +666,10 @@ impl<let NumBytes: u32, let NumPackedFields: u32, let MaxNumTokens: u32, let Max
             scan_mode = scan_token;
         }
 
-        // we encode error flag into the scan_token value, which must be less than 4
+        // we encode error flag into the scan_token value, which must be less than 4 (object, array, string, literal)
         // the lookup into JSON_CAPTURE_TABLE applies an implicit 2-bit range check on `scan_token`
         // however this does not get triggered if the final byte scanned produces an error state
-        length.assert_max_bit_size::<2>();
+        scan_mode.assert_max_bit_size::<2>();
 
         JSON {
             json: self.json,
@@ -689,6 +696,7 @@ impl<let NumBytes: u32, let NumPackedFields: u32, let MaxNumTokens: u32, let Max
         let mut transcript_ptr: u32 = 0;
         // TODO: do we need a null transcript value?!?!
         for i in 0..MaxNumTokens {
+            // encoded_ascii is the encoded scan_mode + ascii character of the LAST token in the entry
             let RawTranscriptEntry { encoded_ascii, index, length } =
                 RawTranscriptEntry::from_field(self.raw_transcript[i]);
 
@@ -722,7 +730,8 @@ impl<let NumBytes: u32, let NumPackedFields: u32, let MaxNumTokens: u32, let Max
      * @brief Check for missing tokens that we could have missed in `build_transcript`
      * @details If we had a json string where a NUMERIC_TOKEN or LITERAL_TOKEN is directly succeeded by a VALUE_SEPARATOR_TOKEN, END_OBJECT_TOKEN, END_ARRAY_TOKEN,
      *          we will have missed the latter token.
-     *          We pick these up via the lookup table PROCESS_RAW_TRANSCRIPT_TABLE
+     *          We pick these up via the lookup table PROCESS_RAW_TRANSCRIPT_TABLE. 
+     *          The entries in self.raw_transcript currently look like false}, true], null, where the grammar tokens are counted as part of the token.
      **/
     fn capture_missing_tokens(&mut self) {
         let mut transcript_ptr: Field = 0;