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| """Display coding costs without changing the arithmetic stream.""" | |
| import html | |
| import math | |
| def token_cost(cdf, token): | |
| probability = int(cdf[token + 1] - cdf[token]) / int(cdf[-1]) | |
| return {'probability': probability, 'bits': -math.log2(probability)} | |
| def text_spans(text, ids, costs, pieces): | |
| """Join byte-split Unicode tokens until they form valid display text.""" | |
| if not len(ids) == len(costs) == len(pieces): | |
| raise ValueError('Token highlight lengths differ.') | |
| if b''.join(pieces) != text.encode('utf-8'): | |
| raise ValueError('Token highlights do not match the original text.') | |
| spans, pending, tokens = [], b'', [] | |
| for token, cost, piece in zip(ids, costs, pieces): | |
| pending += piece | |
| tokens.append({'id': int(token), **cost}) | |
| try: | |
| display = pending.decode('utf-8') | |
| except UnicodeDecodeError: | |
| continue | |
| if not display: | |
| continue | |
| spans.append({'text': display, 'tokens': tokens}) | |
| pending, tokens = b'', [] | |
| if pending or tokens: | |
| raise ValueError('Incomplete token highlight text.') | |
| return spans | |
| # Fixed 2-bit bins make the same cost have the same color across inputs. | |
| COLORS = ['#eef3ec', '#dcebdf', '#bcdcc6', '#8fc3a5', '#388060', '#266a4e', '#13432f'] | |
| def percent(probability): | |
| value = 100 * probability | |
| if value >= 99.95: | |
| return '>99.9%' | |
| if value >= 10: | |
| return f'{value:.0f}%' | |
| if value >= 0.01: | |
| return f'{value:.2g}%' | |
| return '<0.01%' | |
| def describe(tokens): | |
| bits = sum(token['bits'] for token in tokens) | |
| if len(tokens) == 1: | |
| return f'{bits:.2f} bits · p {percent(tokens[0]["probability"])}' | |
| return f'{bits:.2f} bits · {len(tokens)} byte tokens' | |
| def render_highlight(stats): | |
| if not stats or 'token_spans' not in stats: | |
| return '' | |
| parts = [] | |
| for index, span in enumerate(stats['token_spans']): | |
| tokens = span['tokens'] | |
| level = min(6, int(sum(token['bits'] for token in tokens) / len(tokens) / 2)) | |
| foreground = '#ffffff' if level >= 4 else '#1d201c' | |
| # Leading spaces sit outside the shading so words read naturally; the tooltip restores them. | |
| text = span['text'] | |
| body = text.lstrip(' ') | |
| if not body.strip(): | |
| body = text | |
| lead = text[:len(text) - len(body)] | |
| # Line breaks have no width, so a leading one gets a visible mark. | |
| newline = ' data-newline' if body.startswith('\n') else '' | |
| space = f' data-space="{len(lead)}"' if lead else '' | |
| parts.append( | |
| f'{lead}<span class="cost-token" tabindex="{0 if index == 0 else -1}"{newline}{space} ' | |
| f'data-tip="{html.escape(describe(tokens), quote=True)}" ' | |
| f'style="background:{COLORS[level]};color:{foreground}">' | |
| f'{html.escape(body)}</span>' | |
| ) | |
| swatches = ''.join(f'<i style="background:{color}"></i>' for color in COLORS) | |
| body = ''.join(parts) or '<span class="quiet">Empty input has no tokens.</span>' | |
| return ( | |
| '<section class="analysis"><div class="analysis-heading"><h2>Token costs</h2>' | |
| f'<div class="legend" aria-hidden="true"><span>0</span>{swatches}<span>12+ bits</span></div></div>' | |
| '<p class="analysis-hint">Darker tokens took more bits to encode. Hover or tap one to inspect it.</p>' | |
| f'<div class="token-text" aria-label="Original text with token costs">{body}</div>' | |
| '<details class="fine-print"><summary>How to read this</summary>' | |
| '<p>Cost is −log₂ p, using the exact integer probabilities sent to the arithmetic coder. ' | |
| 'These are ideal token costs; the copied code also includes framing and ASCII overhead. ' | |
| 'A character split across several byte tokens is shaded by their average cost.</p></details></section>' | |
| ) | |