compressBound_z
Calculates the numeric bound used to size a default zlib compression buffer.
Full chapter and shared rules ↗767fa1407a7fe3d1 · Source at the matching commit ↗Read the function’s preconditions and results first. Expand the shared rules below for buffer and ownership requirements used throughout this API group.
z_size_t ZEXPORT compressBound_z(z_size_t sourceLen);
Calculates the numeric bound used to size a default zlib compression buffer.
Domain Full type domain.
Pre Full type domain: every 64-bit sourceLen, including zero and the maximum.
Post Returns min(2^64 - 1, n + (n >> 12) + (n >> 14) + (n >> 25) + 13)
for n = sourceLen, with the sum interpreted mathematically. Zero gives 13;
an overflowing sum gives the maximum value.
Effects Pure. No pointer access, allocation, state change or error return.
Scope. This contract specifies the number. Output adequacy is a separate property for valid compression calls with the default wrapper, window and memory settings. It gives no bound for arbitrary raw or gzip stream settings.
Shared conditions and scope
API manual · Shared stream rules · Checksums
Use the buffer utilities when the complete input and output capacity are known at the call. They manage a temporary stream internally. Use the stream pages when you need incremental I/O, a different wrapper, a dictionary or explicit flush boundaries.
| Task | Entries |
|---|---|
| Compress a buffer | Choose a level, default level, size the destination |
| Decompress a buffer | Report input consumed, output only |
| Inspect the library | Version, compile flags, error text |
The focused contracts follow compress.c, uncompr.c, zutil.c and zlib.h in the default
LP64 Linux build. _z forms use z_size_t; plain forms use uLong. Both are 64-bit here.
Source readings are to confirm by proof. They do not narrow the registered targets in
Utilities.lean and
Queries.lean.
Calls.lean fixes translated arguments and results.
See contract conventions for domain/effect labels and
progress for proof status and remaining work.
The buffer utilities create and release a local stream with the zlib wrapper and default settings.
flowchart LR
B["compressBound"] --> C["compress / compress2"]
C --> Z["zlib stream"] --> U["uncompress / uncompress2"]
U --> D["decoded bytes"]
Common conventions
For buffer calls, the domain is restricted to valid memory: non-NULL sources cover the stated readable input; non-NULL destinations cover the stated writable capacity. Non-NULL length pointers name readable, writable scalar cells. Input, output and length cells are separate, including the two length cells when both occur. The caller keeps those objects live and does not modify them during the call. Each entry states its allowed NULL cases. Other invalid pointers are outside this scope. Decompression error handling needs no valid compressed-data assumption.
Common effects. Every in-scope call terminates without a fault. Buffer calls preserve input and memory outside the output and length cells. They write at most the original capacity. All internal allocations are released before return, including on allocation failure; no local stream or owned allocation is returned. Pointer-valued queries return borrowed immutable storage. These are contract requirements, not claims that the implementation proofs are complete.
Formal contract
ZlibF.Spec.Public.Goal.compressBound_z
Proof status: Registered proof · Evidence and remaining work
/-- `z_size_t compressBound_z(z_size_t sourceLen)`.
Every LP64 input returns the saturated public bound formula. No heap is accessed. -/
def Goal.compressBound_z : Prop :=
∀ n : UInt64, (Zlib.Compress.compressBound_z n).toNat = Api.compressBound n.toNat