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/*
 * buf_generic.h -- Macro-template for shared-memory typed buffers.
 *
 * Before including, define:
 *   BUF_PREFIX         -- function prefix (e.g., buf_i64)
 *   BUF_ELEM_TYPE      -- C element type (e.g., int64_t)
 *   BUF_VARIANT_ID     -- unique integer for header validation
 *   BUF_ELEM_SIZE      -- sizeof(BUF_ELEM_TYPE) or fixed string length
 *
 * Optional:
 *   BUF_HAS_COUNTERS   -- generate incr/decr/cas (integer types only)
 *   BUF_IS_FLOAT       -- element is float/double (affects SV conversion)
 *   BUF_IS_FIXEDSTR    -- element is fixed-length char array
 */

/* ================================================================
 * Part 1: Shared definitions (included once)
 * ================================================================ */

#ifndef BUF_DEFS_H
#define BUF_DEFS_H

#include <stdint.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/file.h>
#include <sys/syscall.h>
#include <limits.h>
#include <signal.h>
#include <errno.h>
#include <linux/futex.h>
#include <sys/eventfd.h>
#include <pthread.h>

/* ---- Constants ---- */

#define BUF_MAGIC       0x42554631U  /* "BUF1" */
#define BUF_VERSION     3            /* v3: added occupancy bitmap region (layout change) */
#define BUF_ERR_BUFLEN  256
#define BUF_READER_SLOTS 1024         /* per-process reader-counter mirror */

/* Occupancy bitmap: one bit per reader slot, set when a process claims a slot and
 * cleared on clean release.  A writer scans these BUF_OCC_WORDS words to visit
 * only OCCUPIED slots (O(words + live readers)) instead of all BUF_READER_SLOTS. */
#define BUF_OCC_WORDS   (((BUF_READER_SLOTS) + 63) / 64)   /* 16 for 1024 slots */
#define BUF_OCC_BYTES   ((uint64_t)BUF_OCC_WORDS * 8)      /* 128 bytes */

/* ---- Per-process reader-slot table (in shared memory) ----
 * In the reader-slots-only rwlock a reader's ENTIRE contribution to the shared
 * lock is `rdepth` in its OWN slot -- there is no separate shared reader counter
 * to fall out of sync with it -- so a dead reader's contribution is exactly this
 * one word, which a draining writer neutralises by clearing the slot's pid (the
 * scan then ignores the slot).  No orphaned counter can exist, so there is no
 * quiescent force-reset and sustained readers cannot starve a writer.
 * _rsv1/_rsv2 are kept only to preserve the 16-byte slot size across the
 * already-released builds. */
typedef struct {