util_sha512h

Summary. Compute the SHA-512Half of a buffer — the first 32 bytes of the SHA-512 digest. This is the hashing primitive Xahau uses throughout (ledger hashes, transaction IDs, and, when combined with a namespace prefix, keylet indices).

Signature.

int64_t util_sha512h(
    uint32_t write_ptr,   // 32-byte output buffer
    uint32_t write_len,   // must be >= 32
    uint32_t read_ptr,    // input data
    uint32_t read_len);   // input length

Parameters.

Name	Meaning
write_ptr, write_len	Output buffer. write_len must be at least 32; exactly 32 bytes are written.
read_ptr, read_len	Input data of any length within memory bounds.

Return value. On success, 32 (bytes written). Errors:

Code	Value	Cause
TOO_SMALL	-4	write_len < 32.
OUT_OF_BOUNDS	-1	A region is out of bounds.

Common failure patterns.

• Sizing the output buffer at 64 bytes and assuming a full SHA-512 — only the first 32 bytes (SHA-512Half) are produced.
• If write_len < 32, the wrapper returns TOO_SMALL before checking either memory region for bounds errors.

Caveats. SHA-512Half ≠ SHA-256. Do not use this where a counterpart expects a plain SHA-256 or full SHA-512 digest.

Minimal example.

uint8_t hash[32];
int64_t r = util_sha512h(SBUF(hash), SBUF("hello world"));
if (r != 32)
    rollback(SBUF("hash failed"), r);

Related APIs. util_verify, util_keylet, ledger_nonce.