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| /* -------------------------------------------------------------- */ |
| /* PROLOG END TAG zYx */ |
| #ifdef __SPU__ |
| #ifndef _SQRTF4_H_ |
| #define _SQRTF4_H_ 1 |
| |
| #include <spu_intrinsics.h> |
| |
| /* |
| * FUNCTION |
| * vector float _sqrtf4(vector float in) |
| * |
| * DESCRIPTION |
| * The _sqrtf4 function computes the square root of the vector input "in" |
| *and returns the result. |
| * |
| */ |
| static __inline vector float _sqrtf4(vector float in) |
| { |
| vec_uint4 exp, valid; |
| vec_uint4 mask = spu_splats((unsigned int)0xFF000000); |
| vec_uint4 half = spu_splats((unsigned int)0x00800000); |
| vec_float4 one = spu_splats(1.0f); |
| vec_float4 three = spu_splats(3.0f); |
| vec_float4 x, y0, y1, y1_n1, y1_p1, y1_p2, y1_p3; |
| vec_float4 mant, err, err_p1, err_p2, err_p3; |
| vec_float4 out; |
| |
| /* Compute the mantissa of the result seperately from |
| * the exponent to assure complete accuracy over the allowable |
| * input range. The mantissa is computed for inputs in the |
| * range [0.5, 2.0). |
| */ |
| x = spu_sel(in, one, mask); |
| y0 = spu_rsqrte(x); |
| |
| /* Perform one iteration of the Newton-Raphsom method in single precision |
| * arithmetic. |
| */ |
| y1 = spu_mul(spu_nmsub(x, spu_mul(y0, y0), three), |
| spu_mul(y0, (vec_float4)(spu_sub((vec_uint4)(x), half)))); |
| |
| /* Correct the result for possible error. The range of error is -3 to +1. |
| * Identify the extent of the error and correct for it. |
| */ |
| y1_p3 = (vec_float4)spu_add((vec_uint4)(y1), 3); |
| y1_p2 = (vec_float4)spu_add((vec_uint4)(y1), 2); |
| y1_p1 = (vec_float4)spu_add((vec_uint4)(y1), 1); |
| y1_n1 = (vec_float4)spu_add((vec_uint4)(y1), -1); |
| |
| err = spu_nmsub(y1, y1, x); |
| err_p1 = spu_nmsub(y1_p1, y1_p1, x); |
| err_p2 = spu_nmsub(y1_p2, y1_p2, x); |
| err_p3 = spu_nmsub(y1_p3, y1_p3, x); |
| |
| mant = spu_sel(y1_n1, y1, spu_cmpgt((vec_int4)(err), -1)); |
| mant = spu_sel(mant, y1_p1, spu_cmpgt((vec_int4)(err_p1), -1)); |
| mant = spu_sel(mant, y1_p2, spu_cmpgt((vec_int4)(err_p2), -1)); |
| mant = spu_sel(mant, y1_p3, spu_cmpgt((vec_int4)(err_p3), -1)); |
| |
| /* Compute the expected exponent. If the exponent is zero or the input is |
| * negative, then set the result to zero. |
| */ |
| exp = spu_rlmask(spu_add((vec_uint4)(in), (vec_uint4)(one)), -1); |
| |
| valid = spu_cmpgt(spu_and((vec_int4)(in), (vec_int4)(mask)), 0); |
| |
| /* Merge the computed exponent and mantissa. |
| */ |
| out = spu_and(spu_sel(mant, (vec_float4)(exp), spu_splats(0xFF800000)), (vec_float4)(valid)); |
| |
| |
| return (out); |
| |
| } |
| |
| #endif /* _SQRTF4_H_ */ |
| #endif /* __SPU__ */ |