core: build: Add manifest handling

This resolves redundant rebuilds by detecting when there are differences
in a built file.

Signed-off-by: Chloe M. <chloe@aptel.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/core/hash.c b/core/hash.c
new file mode 100644
index 0000000..557e406
--- /dev/null
+++ b/core/hash.c
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2026, Chloe M., et al.
+ * Provided under the BSD-3 clause.
+ */
+
+#include <sys/mman.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include "bop/hash.h"
+
+int
+bop_hash_file(const char *path, char hashres[BOP_HASH_LEN])
+{
+    int fd;
+    size_t len, i;
+    uint8_t hash[SHA256_DIGEST_LENGTH];
+    void *mem;
+
+    if (path == NULL) {
+        return -1;
+    }
+
+    if ((fd = open(path, O_RDONLY)) < 0) {
+        perror("open");
+        return -1;
+    }
+
+    /* Grab the file length */
+    len = lseek(fd, 0, SEEK_END);
+    lseek(fd, 0, SEEK_SET);
+
+    /* Map the file */
+    mem = mmap(
+        NULL,
+        len,
+        PROT_READ,
+        MAP_SHARED,
+        fd,
+        0
+    );
+
+    if (mem == NULL) {
+        perror("mmap");
+        close(fd);
+        return -1;
+    }
+
+    SHA256(mem, len, hash);
+    for (i = 0; i < SHA256_DIGEST_LENGTH; ++i) {
+        sprintf((char *)hashres + i*2, "%02X", hash[i]);
+    }
+    return 0;
+}