First commit

1 files changed, 71 insertions, 0 deletions

diff --git a/src/leb128.c b/src/leb128.c
new file mode 100644
index 0000000..3c3c8a5
--- /dev/null
+++ b/src/leb128.c
@@ -0,0 +1,71 @@
+/*
+ * nanowasm, a tiny WebAssembly/Wasm interpreter
+ * Copyright (C) 2023-2024  Xavier Del Campo Romero
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+#include <nw/leb128.h>
+#include <nw/log.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+
+/* The functions below are (somewhat heavily) modified versions of those
+ * provided by the wac project: https://github.com/kanaka/wac */
+
+/*
+ * Copyright (C) Joel Martin <github@martintribe.org>
+ * The wac project is licensed under the MPL 2.0 (Mozilla Public License
+ * 2.0). The text of the MPL 2.0 license is included below and can be
+ * found at https://www.mozilla.org/MPL/2.0/
+ */
+
+static int read_LEB(FILE *const f, const unsigned maxbits,
+    const bool sign, unsigned long long *const out)
+{
+    unsigned long long result = 0;
+    unsigned shift = 0, bcnt = 0;
+    uint8_t byte;
+
+    for (;;)
+    {
+        if (!fread(&byte, sizeof byte, 1, f))
+            return -1;
+
+        result |= (unsigned long long)(byte & 0x7f) << shift;
+        shift += 7;
+
+        if (!(byte & 0x80))
+            break;
+        else if (++bcnt > (maxbits + 7 - 1) / 7)
+        {
+            LOG("%s: overflow\n", __func__);
+            return -1;
+        }
+    }
+
+    if (sign && (shift < maxbits) && (byte & 0x40))
+        result |= -1ll << shift;
+
+    *out = result;
+    return 0;
+}
+
+int leb128_read_unsigned(FILE *const f, const unsigned maxbits,
+    unsigned long long *const out)
+{
+    return read_LEB(f, maxbits, false, out);
+}
+
+int leb128_read_signed(FILE *const f, const unsigned maxbits,
+    long long *const out)
+{
+    unsigned long long value;
+    const int ret = read_LEB(f, maxbits, true, &value);
+
+    *out = value;
+    return ret;
+}