Constify character handling too #34
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Reviewer's GuideIntroduces compile-time character classification and escape-token lookup tables to replace runtime matching, streamlining the tokenizer’s escape, whitespace, digit, and hexadecimal handling for improved performance and maintainability. Class diagram for updated Tokenizer character handlingclassDiagram
class Tokenizer {
+const ESCAPE_TOKENS: [Option<EventToken>; 256]
+const IS_DIGIT: [bool; 256]
+const IS_WHITESPACE: [bool; 256]
+const IS_HEX_DIGIT: [bool; 256]
+const NUM_TRANSITIONS: [[Option<Num>; 256]; 8]
...
}
Tokenizer --|> BitBucket : uses
Tokenizer --|> DepthCounter : uses
Tokenizer ..> EventToken : escape/char tables
Tokenizer ..> Num : number transitions
Flow diagram for character classification in Tokenizerflowchart TD
A[Input character] --> B{Is whitespace?}
B -- Yes --> C[Use IS_WHITESPACE lookup]
B -- No --> D{Is digit?}
D -- Yes --> E[Use IS_DIGIT lookup]
D -- No --> F{Is hex digit?}
F -- Yes --> G[Use IS_HEX_DIGIT lookup]
F -- No --> H{Is escape char?}
H -- Yes --> I[Use ESCAPE_TOKENS lookup]
H -- No --> J[Other handling]
File-Level Changes
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WalkthroughThe changes introduce compile-time constant lookup tables within the Changes
Sequence Diagram(s)sequenceDiagram
participant Input as Input Byte
participant Tokenizer
participant LookupTables
participant Parser
Input->>Tokenizer: Provide next byte
Tokenizer->>LookupTables: Check IS_WHITESPACE / IS_NON_ZERO_DIGIT / IS_HEX_DIGIT / ESCAPE_TOKENS
LookupTables-->>Tokenizer: Return lookup result
Tokenizer->>Parser: Emit EventToken or error based on lookup and state
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Summary of Changes
Hello @kaidokert, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request significantly optimizes the ujson tokenizer by shifting character classification and escape sequence mapping from runtime computations to compile-time constant lookup tables. This change aims to reduce CPU cycles spent on character analysis during JSON parsing, leading to improved performance and a more efficient tokenizer.
Highlights
- Performance Optimization via Const Tables: Introduced
constlookup tables (ESCAPE_TOKENS,IS_DIGIT,IS_WHITESPACE,IS_HEX_DIGIT) withinpicojson/src/ujson/tokenizer/mod.rs. These tables pre-compute character classifications and escape sequence mappings at compile time, reducing runtime overhead. - Runtime Logic Replacement: Replaced various runtime
matchstatements,matches!macros, and byte range checks (e.g.,b' ' | b'\t' | b'\n' | b'\r'orb'0'..=b'9') with efficient array lookups using the newly introducedconsttables across the tokenizer's state machine. - Streamlined String and Unicode Parsing: Refactored the string escaping and Unicode escape sequence parsing logic to leverage the
ESCAPE_TOKENSandIS_HEX_DIGITtables, simplifying the code and improving character handling efficiency.
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Code Review
This pull request effectively replaces runtime character matching with compile-time lookup tables for escape sequences and character classes. This is a great improvement for both performance and code clarity. The changes are well-implemented. I have one suggestion to improve the maintainability of one of the new checks.
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Code Review
This pull request enhances performance by using compile-time lookup tables for character classification, simplifying escape sequence handling. A suggestion is provided to improve the readability of the hex digit lookup table generation by avoiding variable shadowing.
Summary by Sourcery
Constify character handling in the JSON tokenizer by introducing compile-time lookup tables and replacing dynamic match logic with table lookups
Enhancements:
Summary by CodeRabbit