padding in C structures - libslas

make clean; OPTIMIZE=1 make
rm -f *.[ao]
cc -O3 -funroll-loops -fexpensive-optimizations -ffast-math -DNDEBUG -Wall -Wextra -Wpadded   -c -o libslas.o libslas.c
In file included from libslas.c:57:
./libslas.h:711:33: warning: padding struct 'LIBSLAS_HEADER' with 1 byte to align
      'file_creation_DOY' [-Wpadded]
    uint16_t                    file_creation_DOY;                  /*!< (c...
                                ^
./libslas.h:717:33: warning: padding struct 'LIBSLAS_HEADER' with 1 byte to align
      'point_data_record_length' [-Wpadded]
    uint16_t                    point_data_record_length;           /*!< (a...
                                ^
./libslas.h:720:33: warning: padding struct 'LIBSLAS_HEADER' with 4 bytes to align
      'x_scale_factor' [-Wpadded]
    double                      x_scale_factor;                     /*!< (c...
                                ^
libslas.c:94:21: warning: padding struct 'INTERNAL_LIBSLAS_STRUCT' with 3 bytes to align 'mode'
      [-Wpadded]
  int32_t           mode;                       /*!<  File open mode (LIBSLAS_UPDATE, L...
                    ^
libslas.c:96:21: warning: padding struct 'INTERNAL_LIBSLAS_STRUCT' with 3 bytes to align 'pos'
      [-Wpadded]
  int64_t           pos;                        /*!<  Position of the LAS file pointer ...
                    ^
In file included from libslas.c:57:
./libslas.h:749:33: warning: padding struct 'LIBSLAS_VLR_HEADER' with 1 byte to align
      'record_id' [-Wpadded]
    uint16_t                    record_id;                          /*!< (c...
                                ^
./libslas.h:745:11: warning: padding size of 'LIBSLAS_VLR_HEADER' with 1 byte to alignment
      boundary [-Wpadded]
  typedef struct
          ^
./libslas.h:783:33: warning: padding struct 'LIBSLAS_POINT_DATA' with 6 bytes to align
      'gps_time' [-Wpadded]
    double                      gps_time;                           /*!< (c...
                                ^
./libslas.h:763:11: warning: padding size of 'LIBSLAS_POINT_DATA' with 2 bytes to alignment
      boundary [-Wpadded]
  typedef struct
          ^
9 warnings generated.
ar -r libslas.a libslas.o
ar: creating archive libslas.a