[wasm] Extra LEB utilities to leb-helper.h

src/wasm/leb-helper.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_WASM_LEB_HELPER_H_
+#define V8_WASM_LEB_HELPER_H_
+
+namespace v8 {
+namespace internal {
+namespace wasm {
+
+class LEBHelper {
+ public:
+  // Write a 32-bit unsigned LEB to {dest}, updating {dest} to point after
+  // the last uint8_t written. No safety checks.
+  static void write_u32v(uint8_t** dest, uint32_t val) {
+    while (val >= 0x80) {
+      *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F));
+      val >>= 7;
+    }
+    *((*dest)++) = static_cast<uint8_t>(val & 0x7F);
+  }
+
+  // Write a 32-bit signed LEB to {dest}, updating {dest} to point after
+  // the last uint8_t written. No safety checks.
+  static void write_i32v(uint8_t** dest, int32_t val) {
+    if (val >= 0) {
+      while (val >= 0x40) {  // prevent sign extension.
+        *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F));
+        val >>= 7;
+      }
+      *((*dest)++) = static_cast<uint8_t>(val & 0xFF);
+    } else {
+      while ((val >> 6) != -1) {
+        *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F));
+        val >>= 7;
+      }
+      *((*dest)++) = static_cast<uint8_t>(val & 0x7F);
+    }
+  }
+
+  // Write a 64-bit unsigned LEB to {dest}, updating {dest} to point after
+  // the last uint8_t written. No safety checks.
+  static void write_u64v(uint8_t** dest, uint64_t val) {
+    while (val >= 0x80) {
+      *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F));
+      val >>= 7;
+    }
+    *((*dest)++) = static_cast<uint8_t>(val & 0x7F);
+  }
+
+  // Write a 64-bit signed LEB to {dest}, updating {dest} to point after
+  // the last uint8_t written. No safety checks.
+  static void write_i64v(uint8_t** dest, int64_t val) {
+    if (val >= 0) {
+      while (val >= 0x40) {  // prevent sign extension.
+        *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F));
+        val >>= 7;
+      }
+      *((*dest)++) = static_cast<uint8_t>(val & 0xFF);
+    } else {
+      while ((val >> 6) != -1) {
+        *((*dest)++) = static_cast<uint8_t>(0x80 | (val & 0x7F));
+        val >>= 7;
+      }
+      *((*dest)++) = static_cast<uint8_t>(val & 0x7F);
+    }
+  }
+
+  // TODO(titzer): move core logic for decoding LEBs from decoder.h to here.
+
+  // Compute the size of {val} if emitted as an LEB32.
+  static inline size_t sizeof_u32v(size_t val) {
+    size_t size = 0;
+    do {
+      size++;
+      val = val >> 7;
+    } while (val > 0);
+    return size;
+  }
+
+  // Compute the size of {val} if emitted as an LEB32.
+  static inline size_t sizeof_i32v(int32_t val) {
+    size_t size = 1;
+    if (val >= 0) {
+      while (val >= 0x40) {  // prevent sign extension.
+        size++;
+        val >>= 7;
+      }
+    } else {
+      while ((val >> 6) != -1) {
+        size++;
+        val >>= 7;
+      }
+    }
+    return size;
+  }
+
+  // Compute the size of {val} if emitted as an unsigned LEB64.
+  static inline size_t sizeof_u64v(uint64_t val) {
+    size_t size = 0;
+    do {
+      size++;
+      val = val >> 7;
+    } while (val > 0);
+    return size;
+  }
+
+  // Compute the size of {val} if emitted as a signed LEB64.
+  static inline size_t sizeof_i64v(int64_t val) {
+    size_t size = 1;
+    if (val >= 0) {
+      while (val >= 0x40) {  // prevent sign extension.
+        size++;
+        val >>= 7;
+      }
+    } else {
+      while ((val >> 6) != -1) {
+        size++;
+        val >>= 7;
+      }
+    }
+    return size;
+  }
+};
+
+}  // namespace wasm
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_WASM_LEB_HELPER_H_