deploy: 521a084827

features/binary_formats/cbor/index.md

@@ -63,7 +63,11 @@ The mapping is **complete** in the sense that any JSON value type can be convert
 
 NaN/infinity handling
 
-If NaN or Infinity are stored inside a JSON number, they are serialized properly. This behavior differs from the normal JSON serialization which serializes NaN or Infinity to `null`.
+`NaN`, `Infinity`, and `-Infinity` are serialized as a CBOR half-precision float (type 0xF9, 3 bytes total): `NaN` as `0xF9 0x7E 0x00`, `Infinity` as `0xF9 0x7C 0x00`, and `-Infinity` as `0xF9 0xFC 0x00`. This behavior differs from the normal JSON serialization which serializes NaN or Infinity to `null`.
+
+Note
+
+Prior to version 3.13.0, NaN and Infinity were instead serialized as a CBOR double-precision float (type 0xFB, 9 bytes total), because the check used to select a smaller encoding compared magnitudes with NaN, which is always `false` and caused the intended half-precision path to be skipped.
 
 Unused CBOR types
 
@@ -178,6 +182,10 @@ The mapping is **incomplete** in the sense that not all CBOR types can be conver
 - simple values (0xE0..0xF3, 0xF8)
 - undefined (0xF7)
 
+Negative integer overflow
+
+CBOR negative integers (major type 1) are decoded as `-1 - n`. If the encoded magnitude `n` is too large for the result to fit into `number_integer_t` (`std::int64_t` by default), parsing fails with a [`parse_error.112`](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112) exception rather than overflowing silently.
+
 Object keys
 
 CBOR allows map keys of any type, whereas JSON only allows strings as keys in object values. Therefore, CBOR maps with keys other than UTF-8 strings are rejected.