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Eric Coissac
8c7017a99d
- Update obioptions.Version from "Release 4.4.29" to "/v/ Release v5" - Update version.txt from 4.29 → .30 (automated by Makefile)
28 lines
1.5 KiB
Markdown
28 lines
1.5 KiB
Markdown
# `InPlaceToLower` Function — Semantic Description
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The `obiutils.InPlaceToLower` function provides a high-performance, memory-efficient utility for converting ASCII uppercase letters to lowercase **in place**, without allocating new data structures.
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## Core Functionality
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- Takes a `[]byte` slice (`data`) as input.
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- Iterates over each byte, identifying uppercase ASCII characters (i.e., `'A'`–`'Z'`, values `65`–`90`).
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- Converts each uppercase byte to its lowercase counterpart using a bitwise OR with `32`, leveraging the ASCII encoding property:
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`lowercase = uppercase | 0b0010_0000` (since `'a' - 'A' = 32`).
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- Returns the **same** `[]byte` slice, now mutated in-place.
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## Key Characteristics
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- ✅ **Zero-copy**: No new memory is allocated—ideal for performance-critical or low-level contexts (e.g., streaming, embedded systems).
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- ✅ **ASCII-safe**: Only modifies bytes in the `'A'`–`'Z'` range; other bytes (e.g., digits, symbols, non-ASCII) remain unchanged.
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- ✅ **Idiomatic Go**: Uses idioms like `range` with index/value and bitwise optimization.
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- ⚠️ **Destructive**: Input data is permanently modified—callers must clone if preservation is needed.
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## Use Cases
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- Preprocessing raw HTTP headers or payloads.
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- Optimizing case-insensitive comparisons in high-throughput systems.
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- Embedded tools where GC pressure or heap allocation must be minimized.
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## Example
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```go
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buf := []byte("HTTP/1.1 200 OK")
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InPlaceToLower(buf) // buf is now []byte("http/1.1 200 ok")
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```
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