AMSS-NCKU/AMSS_NCKU_source/mpi_stub.h

#ifndef MPI_STUB_H
#define MPI_STUB_H

/*
 * MPI Stub Header — single-process shim for AMSS-NCKU ABE solver.
 * Provides all MPI types, constants, and functions used in the codebase
 * as no-ops or trivial implementations for nprocs=1, myrank=0.
 */

#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <time.h>

/* ── Types ─────────────────────────────────────────────────────────── */

typedef int MPI_Comm;
typedef int MPI_Datatype;
typedef int MPI_Op;
typedef int MPI_Request;
typedef int MPI_Group;

typedef struct MPI_Status {
    int MPI_SOURCE;
    int MPI_TAG;
    int MPI_ERROR;
} MPI_Status;

/* ── Constants ─────────────────────────────────────────────────────── */

#define MPI_COMM_WORLD  0

#define MPI_INT              1
#define MPI_DOUBLE           2
#define MPI_DOUBLE_PRECISION 2
#define MPI_DOUBLE_INT       3

#define MPI_SUM    1
#define MPI_MAX    2
#define MPI_MAXLOC 3

#define MPI_STATUS_IGNORE   ((MPI_Status *)0)
#define MPI_STATUSES_IGNORE ((MPI_Status *)0)

#define MPI_MAX_PROCESSOR_NAME 256

/* ── Helper: sizeof for MPI_Datatype ──────────────────────────────── */

static inline size_t mpi_stub_sizeof(MPI_Datatype type) {
    switch (type) {
        case MPI_INT:        return sizeof(int);
        case MPI_DOUBLE:     return sizeof(double);
        case MPI_DOUBLE_INT: return sizeof(double) + sizeof(int);
        default:             return 0;
    }
}

/* ── Init / Finalize ──────────────────────────────────────────────── */

static inline int MPI_Init(int *, char ***) { return 0; }
static inline int MPI_Finalize() { return 0; }

/* ── Communicator queries ─────────────────────────────────────────── */

static inline int MPI_Comm_rank(MPI_Comm, int *rank) { *rank = 0; return 0; }
static inline int MPI_Comm_size(MPI_Comm, int *size) { *size = 1; return 0; }
static inline int MPI_Comm_split(MPI_Comm comm, int, int, MPI_Comm *newcomm) {
    *newcomm = comm;
    return 0;
}
static inline int MPI_Comm_free(MPI_Comm *) { return 0; }

/* ── Group operations ─────────────────────────────────────────────── */

static inline int MPI_Comm_group(MPI_Comm, MPI_Group *group) {
    *group = 0;
    return 0;
}
static inline int MPI_Group_translate_ranks(MPI_Group, int n,
        const int *ranks1, MPI_Group, int *ranks2) {
    for (int i = 0; i < n; ++i) ranks2[i] = ranks1[i];
    return 0;
}
static inline int MPI_Group_free(MPI_Group *) { return 0; }

/* ── Collective operations ────────────────────────────────────────── */

static inline int MPI_Allreduce(const void *sendbuf, void *recvbuf,
        int count, MPI_Datatype datatype, MPI_Op, MPI_Comm) {
    std::memcpy(recvbuf, sendbuf, count * mpi_stub_sizeof(datatype));
    return 0;
}

static inline int MPI_Iallreduce(const void *sendbuf, void *recvbuf,
        int count, MPI_Datatype datatype, MPI_Op, MPI_Comm,
        MPI_Request *request) {
    std::memcpy(recvbuf, sendbuf, count * mpi_stub_sizeof(datatype));
    *request = 0;
    return 0;
}

static inline int MPI_Bcast(void *, int, MPI_Datatype, int, MPI_Comm) {
    return 0;
}

static inline int MPI_Barrier(MPI_Comm) { return 0; }

/* ── Point-to-point (never reached with nprocs=1) ─────────────────── */

static inline int MPI_Send(const void *, int, MPI_Datatype, int, int, MPI_Comm) {
    return 0;
}
static inline int MPI_Recv(void *, int, MPI_Datatype, int, int, MPI_Comm, MPI_Status *) {
    return 0;
}
static inline int MPI_Isend(const void *, int, MPI_Datatype, int, int, MPI_Comm,
        MPI_Request *req) {
    *req = 0;
    return 0;
}
static inline int MPI_Irecv(void *, int, MPI_Datatype, int, int, MPI_Comm,
        MPI_Request *req) {
    *req = 0;
    return 0;
}

/* ── Completion ───────────────────────────────────────────────────── */

static inline int MPI_Wait(MPI_Request *, MPI_Status *) { return 0; }
static inline int MPI_Waitall(int, MPI_Request *, MPI_Status *) { return 0; }

/* ── Utility ──────────────────────────────────────────────────────── */

static inline int MPI_Abort(MPI_Comm, int error_code) {
    std::fprintf(stderr, "MPI_Abort called with error code %d\n", error_code);
    std::exit(error_code);
    return 0;
}

static inline double MPI_Wtime() {
    struct timespec ts;
    clock_gettime(CLOCK_MONOTONIC, &ts);
    return (double)ts.tv_sec + (double)ts.tv_nsec * 1.0e-9;
}

static inline int MPI_Get_processor_name(char *name, int *resultlen) {
    const char *stub_name = "localhost";
    std::strcpy(name, stub_name);
    *resultlen = (int)std::strlen(stub_name);
    return 0;
}

#endif /* MPI_STUB_H */