avr-gcc global var as constant

///////////////////////////////////////////////////////////////////////////////
/// @file bitreverse.c
/// @brief bitreverse implementation for atmega processors
/// @date 2014.09.02
///
/// @version
///     0.1.0 2014.09.02
///////////////////////////////////////////////////////////////////////////////
#include"bitreverse.h"
#define TEST
///////////////////////////////////////////////////////////////////////////////
/// @var BitReverseTable
/// @brief Lookup table with the reversed bits
///
/// the bit reversed lookup table is placed in \c progmem and is alligned at
/// the beginning of a 0x100 byte block to speed up the access.
///////////////////////////////////////////////////////////////////////////////
uint8_t BitReverseTable[]
            __attribute__((__progmem__, aligned(0x100))) = {
    0x00,0x80,0x40,0xC0,0x20,0xA0,0x60,0xE0,
    0x10,0x90,0x50,0xD0,0x30,0xB0,0x70,0xF0,
    0x08,0x88,0x48,0xC8,0x28,0xA8,0x68,0xE8,
    0x18,0x98,0x58,0xD8,0x38,0xB8,0x78,0xF8,
    0x04,0x84,0x44,0xC4,0x24,0xA4,0x64,0xE4,
    0x14,0x94,0x54,0xD4,0x34,0xB4,0x74,0xF4,
    0x0C,0x8C,0x4C,0xCC,0x2C,0xAC,0x6C,0xEC,
    0x1C,0x9C,0x5C,0xDC,0x3C,0xBC,0x7C,0xFC,
    0x02,0x82,0x42,0xC2,0x22,0xA2,0x62,0xE2,
    0x12,0x92,0x52,0xD2,0x32,0xB2,0x72,0xF2,
    0x0A,0x8A,0x4A,0xCA,0x2A,0xAA,0x6A,0xEA,
    0x1A,0x9A,0x5A,0xDA,0x3A,0xBA,0x7A,0xFA,
    0x06,0x86,0x46,0xC6,0x26,0xA6,0x66,0xE6,
    0x16,0x96,0x56,0xD6,0x36,0xB6,0x76,0xF6,
    0x0E,0x8E,0x4E,0xCE,0x2E,0xAE,0x6E,0xEE,
    0x1E,0x9E,0x5E,0xDE,0x3E,0xBE,0x7E,0xFE,
    0x01,0x81,0x41,0xC1,0x21,0xA1,0x61,0xE1,
    0x11,0x91,0x51,0xD1,0x31,0xB1,0x71,0xF1,
    0x09,0x89,0x49,0xC9,0x29,0xA9,0x69,0xE9,
    0x19,0x99,0x59,0xD9,0x39,0xB9,0x79,0xF9,
    0x05,0x85,0x45,0xC5,0x25,0xA5,0x65,0xE5,
    0x15,0x95,0x55,0xD5,0x35,0xB5,0x75,0xF5,
    0x0D,0x8D,0x4D,0xCD,0x2D,0xAD,0x6D,0xED,
    0x1D,0x9D,0x5D,0xDD,0x3D,0xBD,0x7D,0xFD,
    0x03,0x83,0x43,0xC3,0x23,0xA3,0x63,0xE3,
    0x13,0x93,0x53,0xD3,0x33,0xB3,0x73,0xF3,
    0x0B,0x8B,0x4B,0xCB,0x2B,0xAB,0x6B,0xEB,
    0x1B,0x9B,0x5B,0xDB,0x3B,0xBB,0x7B,0xFB,
    0x07,0x87,0x47,0xC7,0x27,0xA7,0x67,0xE7,
    0x17,0x97,0x57,0xD7,0x37,0xB7,0x77,0xF7,
    0x0F,0x8F,0x4F,0xCF,0x2F,0xAF,0x6F,0xEF,
    0x1F,0x9F,0x5F,0xDF,0x3F,0xBF,0x7F,0xFF
};
///////////////////////////////////////////////////////////////////////////////
#define BITREVERSE(x) (__extension__({                                        \
    register uint8_t b=(uint8_t)x;                                            \
    __asm__ __volatile__ (                                                    \
        "ldi r31, hi8(table)"                                          "\n\t" \
        "mov r30, ioRegister"                                          "\n\t" \
        "lpm ioRegister, z"                                            "\n\t" \
        :[ioRegister] "+r" (b)                                                \
        :[table] "g" (BitReverseTable)                                        \
        :"r30", "r31"                                                         \
    );                                                                        \
}))
///////////////////////////////////////////////////////////////////////////////
#ifdef TEST
int main() ///
{
    BITREVERSE(25);
    return 0;
}
#endif
///////////////////////////////////////////////////////////////////////////////
/////////////////////////////// END of FILE ///////////////////////////////////
///////////////////////////////////////////////////////////////////////////////