lookup.dart

import 'dart:io';
import 'dart:typed_data';
import 'dart:convert';

const int FIBONACCI_CONSTANT = 2654435769;

int h24(String s) {
  const int FNV_OFFSET_BASIS = 2166136261;
  const int FNV_PRIME = 16777619;
  int h = FNV_OFFSET_BASIS;
  for (final b in utf8.encode(s)) {
    h ^= b;
    h = (h * FNV_PRIME) & 0xFFFFFFFF;
  }
  final v = h >> 8;
  return v == 0 ? 1 : v;
}

int slotIndex(int key, int capacity) => (key * FIBONACCI_CONSTANT) & (capacity - 1);

void main(List<String> args) {
  if (args.isEmpty) {
    stdout.writeln('Usage: dart run <script.dart> <name>');
    exit(1);
  }
  final name = args[0];
  final path = 'output/py_call_freq.7.bin';
  final file = File(path);
  if (!file.existsSync()) {
    stderr.writeln('file not found: $path');
    exit(2);
  }

  final bytes = file.readAsBytesSync();
  if (bytes.length < 16) {
    stderr.writeln('corrupt or truncated file');
    exit(3);
  }

  final bd = ByteData.sublistView(bytes);
  var offset = 0;
  final magic = bd.getUint32(offset, Endian.little);
  offset += 4;
  if (magic != 0x48534354) {
    stderr.writeln('bad magic number: 0x${magic.toRadixString(16)}');
    exit(4);
  }
  offset += 8;
  final capacity = bd.getUint32(offset, Endian.little);
  offset += 4;

  if (bytes.length < offset + capacity * 4) {
    stderr.writeln('corrupt or truncated slots section');
    exit(5);
  }

  final slots = List<int>.generate(capacity, (i) => bd.getUint32(offset + i * 4, Endian.little));

  final key = h24(name);
  var i = slotIndex(key, capacity);
  final mask = capacity - 1;

  for (var probes = 0; probes < capacity; probes++) {
    final slot = slots[i];
    if (slot == 0) {
      stdout.writeln('$name: not found');
      exit(0);
    }
    final slotKey = slot >> 8;
    final score = slot & 0xFF;
    if (slotKey == key) {
      stdout.writeln('$name: score=$score');
      exit(0);
    }
    i = (i + 1) & mask;
  }

  stdout.writeln('$name: not found');
}