Module offset_evaluator

Bit-Packed Offset Evaluator

This is the part that automatically determines the offsets (and in the future lengths) of the data we’re processing based on a set of simple rules. This is the magic that allows us to throw files like .DDS without manually stripping the unwanted metadata.

What It Does

• Finds data structures based on simple byte checks
• Handles both MSB and LSB bit order formats
• Works with file streams or in-memory byte slices
• Can be used to validate file headers and exclude unwanted data

Public API

Main Types

• ConditionalOffset: Defines conditions for offset evaluation
• Condition: Individual condition for bit pattern matching

Key Functions

• try_evaluate_file_offset(): Find offset in file
• try_evaluate_offset(): Find offset in byte slice

Example Usage

Evaluate an offset for sample data.

use struct_compression_analyzer::offset_evaluator::try_evaluate_offset;
use struct_compression_analyzer::schema::{BitOrder, Condition, ConditionalOffset};

let mut sample_data = vec![0u8; 0x80 + 4];
// Set DDS magic
sample_data[0x00..0x04].copy_from_slice(&[0x44, 0x44, 0x53, 0x20]);
// Set DX10 header
sample_data[0x54..0x58].copy_from_slice(&[0x44, 0x58, 0x31, 0x30]);

// DDS with DX10 header (BC7, BC6H etc.)
let conditions = vec![ConditionalOffset {
    offset: 0x94, // Offset to jump to (DX10 block data)
    conditions: vec![
        Condition {
            byte_offset: 0, // File Magic
            bit_offset: 0,
            bits: 32,
            value: 0x44445320, // DDS magic
            bit_order: BitOrder::Msb,
        },
        Condition {
            byte_offset: 0x54,
            bit_offset: 0,
            bits: 32,
            value: 0x44583130, // 'DX10' fourCC code
            bit_order: BitOrder::Msb,
        },
    ],
}];

let result = try_evaluate_offset(&conditions, &sample_data);
assert_eq!(result, Some(0x94));

Functions

try_evaluate_file_offset

try_evaluate_offset