nextafterf4.h

Newlib 嵌入式 C库 标准实现代码

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/* PROLOG END TAG zYx                                              */
#ifdef __SPU__
#ifndef _NEXTAFTERF4_H_
#define _NEXTAFTERF4_H_	1

#include <spu_intrinsics.h>

/*
 * FUNCTION
 *  vector float _nextafterf4(vector float x, vector float y)
 *
 * DESCRIPTION
 *  The nextafterf4 function returns a vector containing the next representable
 *  floating-point number after the element of x, in the direction of the
 *  corresponding element y. 
 *
 *  Special Cases:
 *	- Infinity and NaN are not supported in single-precision on SPU. They are treated
 *	  as normal numbers.
 *	- x != y, and result = 0 is considered an underflow.
 *	  
 *
 */

static __inline vector float _nextafterf4(vector float x, vector float y)
{
    vec_float4 n1ulp = (vec_float4)spu_splats(0x80000001);
    vec_float4 zerof = spu_splats(0.0f);
    vec_int4  one    = spu_splats(1);
    vec_uint4 xlt0, xgty, xeqy, xeq0;
    vec_int4  xint;
    vec_int4  delta, deltap1;
    vec_float4 result;

    /*
     * The idea here is to treat x as a signed int value, which allows us to
     * add or subtact one to/from it to get the next representable value.
     */

    xeq0 = spu_cmpeq(x, zerof);
    xlt0 = spu_cmpgt(zerof, x);
    xeqy = spu_cmpeq(x, y);
    xgty = spu_cmpgt(x, y);

    /* If x = -0.0, set x = 0.0 */
    x = spu_andc(x, (vec_float4)xeq0);

    xint = (vec_int4)x;

    /* Determine value to add to x */
    delta = (vec_int4)spu_xor(xgty, xlt0);
    deltap1 = delta + one;
    delta = spu_sel(deltap1, delta, (vec_uint4)delta);

    xint = xint + delta;

    /* Fix the case of x = 0, and answer should be -1 ulp */
    result = spu_sel((vec_float4)xint, n1ulp, spu_and((vec_uint4)delta, xeq0));

    /* 
     * Special Cases
     */

    /* x = y */
    result = spu_sel(result, y, xeqy);

    return result;

}

#endif /* _NEXTAFTERF4_H_ */
#endif /* __SPU__ */