Floyd Warshall All Pairs Shortest Paths in C

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <limits.h>
#include <errno.h>
// Floyd Warshall All Pairs Shortest Paths in C
//
// PURPOSE
// Floyd-Warshall computes distances between every pair by gradually allowing more
// intermediate vertices. The ordering of the three loops expresses the dynamic programming
// recurrence.
//
// METHOD
// For each intermediate k, try improving every i-to-j path through k. Skip unreachable
// halves before adding distances. After pass k, paths may use only intermediates up to k.
//
// COMPLEXITY
// O(n cubed) time and O(1) auxiliary space beyond the caller-owned n squared distance
// matrix.
//
// CONTRACT
// Mutates flattened distance matrix. Diagonal starts at 0; missing edges use 1,000,000,000.
// Negative edges allowed. Finite path sums must fit and remain strictly between -INF and
// INF. Returns -1 if any negative cycle exists, otherwise 0.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// C99: checked calloc/free workspace, const input pointers, explicit size_t lengths. Errors
// return INT_MIN with errno=EINVAL, ERANGE, or ENOMEM. Check errno before using a result.
// Input/output arrays must not alias. No variable-length stack arrays.
//
// EXAMPLE
// Expected return: 0.
// Expected distance after call: [0, 4, 6, 1000000000, 0, 2, 1000000000, 1000000000, 0].
// Run: gcc -std=c99 -O2 example.c -o example && ./example
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

static int alg_min(int a, int b) { return a < b ? a : b; }
static int alg_max(int a, int b) { return a > b ? a : b; }
static int alg_checked(int64_t v, int *error) {
    if (v < INT_MIN || v > INT_MAX) { *error = 1; return 0; }
    return (int)v;
}
static int alg_add(int a, int b, int *e) { return alg_checked((int64_t)a+b,e); }
static int alg_sub(int a, int b, int *e) { return alg_checked((int64_t)a-b,e); }
static int alg_mul(int a, int b, int *e) { return alg_checked((int64_t)a*b,e); }

int floyd_warshall(int *distance, size_t distance_length, int n) {
    int alg_error = 0;
    int alg_result = INT_MIN;
    errno = 0;
    if (distance_length > 1000000 || (distance_length && !distance)) { errno = EINVAL; alg_result = INT_MIN; goto alg_cleanup; }
    if (!(((n >= 0) && (n <= 1000000)))) { errno = EINVAL; alg_result = INT_MIN; goto alg_cleanup; }
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    if (!(((int)distance_length == alg_mul(n, n, &alg_error)))) { errno = EINVAL; alg_result = INT_MIN; goto alg_cleanup; }
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    int k = 0;
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    int i = 0;
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    int j = 0;
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    while (1) {
        int alg_condition = (k < n);
        if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
        if (!alg_condition) break;
        i = 0;
        if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
        while (1) {
            int alg_condition = (i < n);
            if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
            if (!alg_condition) break;
            j = 0;
            if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
            while (1) {
                int alg_condition = (j < n);
                if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
                if (!alg_condition) break;
                int alg_condition_1 = ((distance[alg_add(alg_mul(i, n, &alg_error), k, &alg_error)] != 1000000000) && (distance[alg_add(alg_mul(k, n, &alg_error), j, &alg_error)] != 1000000000));
                if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
                if (alg_condition_1) {
                    distance[alg_add(alg_mul(i, n, &alg_error), j, &alg_error)] = alg_min(distance[alg_add(alg_mul(i, n, &alg_error), j, &alg_error)], alg_add(distance[alg_add(alg_mul(i, n, &alg_error), k, &alg_error)], distance[alg_add(alg_mul(k, n, &alg_error), j, &alg_error)], &alg_error));
                    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
                }
                j = alg_add(j, 1, &alg_error);
                if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
            }
            i = alg_add(i, 1, &alg_error);
            if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
        }
        k = alg_add(k, 1, &alg_error);
        if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    }
    i = 0;
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    while (1) {
        int alg_condition = (i < n);
        if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
        if (!alg_condition) break;
        int alg_condition_2 = (distance[alg_add(alg_mul(i, n, &alg_error), i, &alg_error)] < 0);
        if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
        if (alg_condition_2) {
            alg_result = alg_sub(0, 1, &alg_error);
            if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
            goto alg_cleanup;
        }
        i = alg_add(i, 1, &alg_error);
        if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    }
    alg_result = 0;
    if (alg_error) { errno = ERANGE; alg_result = INT_MIN; goto alg_cleanup; }
    goto alg_cleanup;
alg_cleanup:
    return alg_result;
}

int main(void) {
    int distance[] = {0, 4, 10, 1000000000, 0, 2, 1000000000, 1000000000, 0};
    int n = 3;
    int result = floyd_warshall(distance, 9, n);
    printf("%d\n", result);
    for (int z = 0; z < 9; z++) printf("%d ", distance[z]);
    printf("\n");
    // Expected distance: [0, 4, 6, 1000000000, 0, 2, 1000000000, 1000000000, 0]
    if (errno) { perror("algorithm"); return 1; }
    return 0;
}