#define FP_BITS         (12)
#define FP_MASK         ((1 << FP_BITS) - 1)
#define FP_ONE          (1 << FP_BITS)
#define FP_TWO          (2 << FP_BITS)
#define FP_HALF         (1 << (FP_BITS - 1))
#define FP_LN2          ( 45426 >> (16 - FP_BITS))
#define FP_LN2_INV      ( 94548 >> (16 - FP_BITS))
#define FP_EXP_ZERO     ( 10922 >> (16 - FP_BITS))
#define FP_EXP_ONE      (  -182 >> (16 - FP_BITS))
#define FP_EXP_TWO      (     4 >> (16 - FP_BITS))
#define FP_INF          (0x7fffffff)
#define FP_LN10         (150902 >> (16 - FP_BITS))

#define FP_MAX_DIGITS       (4)
#define FP_MAX_DIGITS_INT   (10000)

// #define FP_FAST_MUL_DIV

// #ifdef FP_FAST_MUL_DIV

/* These macros can easily overflow, but they are good enough for our uses,
 * and saves some code.
 */
#define fp_mul(x, y) (((x) * (y)) >> FP_BITS)
#define fp_div(x, y) (((x) << FP_BITS) / (y))

#define abs(x) (((x)<0)?((x)*-1):(x))
float spx_exp(float xf){
  long x=((long)xf)<<FP_BITS;
/*
static long fp_exp(long x)
{*/
    long k;
    long z;
    long R;
    long xp;

    if (x == 0)
    {
        return FP_ONE;
    }

    k = (fp_mul(abs(x), FP_LN2_INV) + FP_HALF) & ~FP_MASK;

    if (x < 0)
    {
        k = -k;
    }

    x -= fp_mul(k, FP_LN2);
    z = fp_mul(x, x);
    R = FP_TWO + fp_mul(z, FP_EXP_ZERO + fp_mul(z, FP_EXP_ONE
        + fp_mul(z, FP_EXP_TWO)));
    xp = FP_ONE + fp_div(fp_mul(FP_TWO, x), R - x);

    if (k < 0)
    {
        k = FP_ONE >> (-k >> FP_BITS);
    }
    else
    {
        k = FP_ONE << (k >> FP_BITS);
    }

    return (fp_mul(k, xp)>>FP_BITS);
}