src/tint/utils/text/base64.h

// Copyright 2023 The Dawn & Tint Authors
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#ifndef SRC_TINT_UTILS_TEXT_BASE64_H_
#define SRC_TINT_UTILS_TEXT_BASE64_H_

#include <cstdint>
#include <optional>

namespace tint {

/// Decodes a byte from a base64 encoded character
/// @param c the character to decode
/// @return the decoded value, or std::nullopt if the character is padding ('=') or an invalid
/// character.
inline std::optional<uint8_t> DecodeBase64(char c) {
    if (c >= 'A' && c <= 'Z') {
        return static_cast<uint8_t>(c - 'A');
    }
    if (c >= 'a' && c <= 'z') {
        return static_cast<uint8_t>(26 + c - 'a');
    }
    if (c >= '0' && c <= '9') {
        return static_cast<uint8_t>(52 + c - '0');
    }
    if (c == '+') {
        return 62;
    }
    if (c == '/') {
        return 63;
    }
    return std::nullopt;
}

}  // namespace tint

#endif  // SRC_TINT_UTILS_TEXT_BASE64_H_