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Address the review of the json_view object index and SIMD scan

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From gregmarr's review of #5628:

- Docs and comments say that the hash index is one of the object's keys.
- object_index.hpp: conditional_static_cast for the hash, "slot" for the
  table position, no flag for a degenerate table, and a static_assert
  that the smallest indexed object is larger than the probe window.
- scan.hpp unrolls with NLOHMANN_VIEW_REPEAT_FIRST_8/SECOND_8.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
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Niels Lohmann committed 2026-10-19 22:07:43 +02:00
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commit 87737b4915
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+54 -48
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docs/mkdocs/docs/home/architecture.md
+2 -2
View File
@@ -196,7 +196,7 @@ packet-beta
|-------|---------|------------|-------------------------------------------------------------------------------------------------------------------------------|
| 0 | `kind` | `uint8_t` | the type, numbered as [`value_t`](../api/basic_json/value_t.md): 0 null, 1 object, 2 array, 3 string, 4 boolean, 5 signed integer, 6 unsigned integer, 7 float |
| 1 | `flags` | `uint8_t` | bits 0-1: where a string's bytes are (0: the source text, 1: the buffer of decoded strings, for strings with escapes); bit 2: the value of a boolean |
| 2-3 | `extra` | `uint16_t` | numbers: the number of integer digits (low byte) and fraction digits (high byte), 255 for more; objects: the number of their hash index (1-based), or 0; otherwise 0 |
| 2-3 | `extra` | `uint16_t` | numbers: the number of integer digits (low byte) and fraction digits (high byte), 255 for more; objects: the number of their key hash index (1-based), or 0; otherwise 0 |
| 4-7 | `off` | `uint32_t` | where the value starts: the first byte after a string's opening quote (or its position in the buffer of decoded strings), the first byte of a number or literal, the bracket of an array or object |
| 8-11 | `len` | `uint32_t` | strings: the length after decoding; floats and literals: the length of the token; arrays and objects: the number of elements |
| 12-15 | `next` | `uint32_t` | arrays and objects: the number of nodes of the subtree, including the node itself |
@@ -212,7 +212,7 @@ packet-beta
step from element to element this way and skip whole subtrees in constant time.
- **Offsets** are 32 bits wide, so a document is limited to 4294967279 bytes, 4 GiB minus 16 bytes (a margin below
2^32 for positions one scanner step past the end of the text; `out_of_range.416`).
- **Large objects** (128 members or more) get a hash index after parsing
- **Large objects** (128 members or more) get a hash index for their keys after parsing
([`detail/view/object_index.hpp`](https://github.com/nlohmann/json/blob/develop/include/nlohmann/detail/view/object_index.hpp)):
an open-addressing table whose slots hold the distance from the object's node to a key's node, so that a lookup does
not compare every key. Of duplicate keys the table leads to the first, as a linear search does. The object's `extra`