ZINC.F64

Increments a 64-bit floating-point value in the ZMap ordered key-value store.

Syntax

ZINC.F64 <key> <value>

Parameters

Parameter	Type	Required	Description
key	bytes	Yes	The key to increment.
value	double	Yes	A finite IEEE-754 double to add to the current value. Use a negative number to decrement.

Return Value

Simple string: OK on success.

Behavior

ZINC.F64 performs a floating-point increment on a key in the ZMap subspace of the session’s current namespace. Unlike ZINC.I64, which uses FoundationDB’s conflict-free ADD mutation, ZINC.F64 performs a read-modify-write cycle because FoundationDB has no atomic double-add mutation. This means concurrent ZINC.F64 calls on the same key can cause transaction conflicts.

If the key does not exist, it is created with an implicit starting value of zero and then incremented by value.

The value is encoded as an 8-byte little-endian IEEE-754 double. Three validation guards protect against invalid states:

1. Finite input: the delta must be a finite double; NaN and Infinity are rejected.
2. Valid stored size: if the key already exists, the stored value must be exactly 8 bytes.
3. Finite result: the computed sum must be finite; overflow to Infinity is rejected.

The command normalizes negative zero: if the result is -0.0, it is stored as 0.0.

The command supports two transaction modes:

• Auto-commit (one-off): When no explicit transaction is active, Kronotop creates a transaction, performs the operation, and commits it immediately. This is the default mode.
• Explicit transaction: When a BEGIN has been issued, the operation is staged in the current transaction and only persists when COMMIT is called.

ZINC.F64 is a write operation and does not support snapshot reads.

All data is scoped to the session’s active namespace. The same key in different namespaces refers to different entries.

Errors

ERR is returned when:

• Invalid delta: value must be a finite IEEE-754 double: The provided value is NaN or Infinity.
• Invalid stored value: expected 8-byte IEEE-754 double: The existing value at the key is not 8 bytes.
• Resulting value is not a finite IEEE-754 double (overflow or invalid operation): The sum overflows to Infinity.
• Wrong number of arguments, value is not a valid double, or internal failure.

Examples

Increment a new key (implicit zero start):

> ZINC.F64 counter 10.5
OK

> ZGET.F64 counter
(double) 10.5

Accumulate multiple increments:

> ZINC.F64 counter 1.5
OK

> ZINC.F64 counter 3.0
OK

> ZINC.F64 counter 4.5
OK

> ZGET.F64 counter
(double) 9.0

Decrement with a negative value:

> ZINC.F64 counter 100.0
OK

> ZINC.F64 counter -30.5
OK

> ZGET.F64 counter
(double) 69.5

Overflow rejection:

> ZINC.F64 counter 1.7976931348623157E308
OK

> ZINC.F64 counter 1.7976931348623157E308
(error) ERR Resulting value is not a finite IEEE-754 double (overflow or invalid operation)

Use within an explicit transaction:

> BEGIN
OK

> ZINC.F64 tx-counter 42.42
OK

> COMMIT
OK

> ZGET.F64 tx-counter
(double) 42.42