Import of the watch repository from Pebble

src/fw/util/sle.c

@@ -0,0 +1,64 @@
+/*
+ * Copyright 2024 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "sle.h"
+
+#include "system/passert.h"
+
+// See waftools/sparse_length_encoding.py for more info on SLE encoding/decoding
+
+void sle_decode_init(SLEDecodeContext *ctx, const void *sle_buffer) {
+  PBL_ASSERTN(ctx && sle_buffer);
+  const uint8_t *buffer = (const uint8_t *)sle_buffer;
+  ctx->escape = *(buffer++);
+  ctx->sle_buffer = buffer;
+  ctx->zeros_remaining = 0;
+}
+
+bool sle_decode(SLEDecodeContext *ctx, uint8_t *out) {
+  if (!ctx->sle_buffer) {
+    return false;
+  }
+  if (ctx->zeros_remaining) {
+    *out = 0;
+    --ctx->zeros_remaining;
+    return true;
+  }
+  uint8_t byte = *(ctx->sle_buffer++);
+  if (byte != ctx->escape) {
+    *out = byte;
+  } else {
+    byte = *(ctx->sle_buffer++);
+    if (byte == 0x00) {
+      // end of stream
+      ctx->sle_buffer = NULL;
+      return false;
+    } else if (byte == 0x01) {
+      // literal escape byte
+      *out = ctx->escape;
+    } else {
+      // a sequence of zeros
+      if ((byte & 0x80) == 0) {
+        // the count is 1 byte (1-127)
+        ctx->zeros_remaining = byte - 1;
+      } else {
+        ctx->zeros_remaining = (((byte & 0x7f) << 8) | *(ctx->sle_buffer++)) + 0x80 - 1;
+      }
+      *out = 0;
+    }
+  }
+  return true;
+}