adler32_z
Update an Adler-32 checksum with a byte range, or obtain its initial value.
Full chapter and shared rules ↗57ad356e10ec68ee · 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.
uLong ZEXPORT adler32_z(uLong adler, const Bytef *buf, z_size_t len);
Update an Adler-32 checksum with a byte range, or obtain its initial value.
Domain Restricted domain. Effects: read-only when buf is non-NULL.
Pre Either buf is NULL and len == 0, or it points to len readable
bytes. For the checksum postcondition, the low 32 bits of adler are the Adler-32 of A.
There is no setup or cleanup requirement.
Post A NULL, zero-length query returns 1 for every adler, without reading
bytes. Otherwise return the Adler-32 of A followed by buf[0..len-1].
A non-NULL zero-length range returns the incoming checksum's low 32 bits.
Effects Preserve all memory and ownership. Read only the given range. A one-past pointer is allowed for a zero-length range.
NULL with nonzero length is outside this contract. Forged seeds remain outside this practical functional contract: the one-byte path need not agree with first reducing both seed halves modulo 65521. See the Adler seed note.
Shared conditions and scope
API manual · Contract conventions · Buffer utilities
Compute a checksum a buffer at a time, or combine the checksums of independently processed byte sequences without rereading them. The byte sequences A and B below are ordinary data; the contracts use the Adler-32 or CRC-32 of those sequences.
| Task | Entries |
|---|---|
| Update Adler-32 | Size-type length, 32-bit length |
| Combine Adler-32 | Ordinary offset, explicit 64-bit offset |
| Update CRC-32 | Size-type length, 32-bit length |
| Combine CRC-32 | Ordinary offset, explicit 64-bit offset |
| Reuse a CRC combination operator | Generate, generate with 64-bit length, apply |
| Inspect the byte table | get_crc_table |
These focused contracts follow adler32.c, crc32.c and zlib.h in the default LP64 Linux
static build, with the pinned source and listed patches. Source readings are to confirm
by proof. No checksum entry writes state, allocates, frees or performs I/O. Exceptional
numeric results are ordinary values, rather than error codes. Domain and effects remain
independent as explained in contract conventions.
The practical checksum contracts use actual byte sequences A and B. Each checksum is computed independently, starting at 1 for Adler-32 or 0 for CRC-32. These contracts deliberately omit functional promises for forged checksums. The Lean targets also describe arbitrary seeds and exact scalar results. Both the Adler entries and their Lean targets require zero length for NULL initialization queries. See scope deviations and public goals.
In this build, uLong and z_size_t are unsigned 64-bit types; uInt is
unsigned 32-bit. z_off_t and z_off64_t are signed 64-bit. Input checksum bits
above bit 31 are ignored; returned checksums fit in 32 bits. The explicit
*64 declarations depend on the header's large-file feature macros.
Formal contract
ZlibF.Spec.Public.Goal.adler32_z
Proof status: Registered proof · Evidence and remaining work
/-- `uLong adler32_z(uLong adler, const Bytef *buf, z_size_t len)`.
NULL queries have zero length; nonnull readable objects cover 64-bit lengths and all seeds.
See `docs/deviations.md` for the query restriction. Exact value, no fault, termination,
no allocation and the complete heap frame. -/
def Goal.adler32_z : Prop := AdlerUpdate Zlib.Adler32.adler32_z