Support whisper models (#238)

sherpa-onnx/csrc/base64-decode.cc

@@ -0,0 +1,67 @@
+// sherpa-onnx/csrc/base64-decode.cc
+//
+// Copyright (c)  2022-2023  Xiaomi Corporation
+
+#include "sherpa-onnx/csrc/base64-decode.h"
+
+#include "sherpa-onnx/csrc/macros.h"
+
+namespace sherpa_onnx {
+
+static int32_t Ord(char c) {
+  if (c >= 'A' && c <= 'Z') {
+    return c - 'A';
+  } else if (c >= 'a' && c <= 'z') {
+    return c - 'a' + ('Z' - 'A') + 1;
+  } else if (c >= '0' && c <= '9') {
+    return c - '0' + ('Z' - 'A') + ('z' - 'a') + 2;
+  } else if (c == '+') {
+    return 62;
+  } else if (c == '/') {
+    return 63;
+  }
+
+  SHERPA_ONNX_LOGE("Unknown character %d, %c\n", c, c);
+
+  exit(-1);
+}
+
+// see
+// https://github.com/ReneNyffenegger/cpp-base64/blob/master/base64.cpp#L243
+std::string Base64Decode(const std::string &s) {
+  if (s.empty()) {
+    SHERPA_ONNX_LOGE("Empty string!");
+    exit(-1);
+  }
+
+  int32_t n = s.size() / 4 * 3;
+
+  std::string ans;
+  ans.reserve(n);
+
+  int32_t i = 0;
+  while (i < static_cast<int32_t>(s.size())) {
+    if (s[i] == '=') {
+      return " ";
+    }
+
+    int32_t first = (Ord(s[i]) << 2) + ((Ord(s[i + 1]) & 0x30) >> 4);
+    ans.push_back(first);
+
+    if (i + 2 < static_cast<int32_t>(s.size()) && s[i + 2] != '=') {
+      int32_t second =
+          ((Ord(s[i + 1]) & 0x0f) << 4) + ((Ord(s[i + 2]) & 0x3c) >> 2);
+      ans.push_back(second);
+
+      if (i + 3 < static_cast<int32_t>(s.size()) && s[i + 3] != '=') {
+        int32_t third = ((Ord(s[i + 2]) & 0x03) << 6) + Ord(s[i + 3]);
+        ans.push_back(third);
+      }
+    }
+    i += 4;
+  }
+
+  return ans;
+}
+
+}  // namespace sherpa_onnx