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| /* PROLOG END TAG zYx */ |
| #ifdef __SPU__ |
| #ifndef _EXP2F4_H_ |
| #define _EXP2F4_H_ 1 |
| |
| |
| #include <spu_intrinsics.h> |
| #include "simdmath.h" |
| |
| /* |
| * FUNCTION |
| * vector float _exp2f4(vector float x) |
| * |
| * DESCRIPTION |
| * The _exp2f4 function computes 2 raised to the input vector x. |
| * Computation is performed by observing the 2^(a+b) = 2^a * 2^b. |
| * We decompose x into a and b (above) by letting. |
| * a = ceil(x), b = x - a; |
| * |
| * 2^a is easilty computed by placing a into the exponent |
| * or a floating point number whose mantissa is all zeros. |
| * |
| * 2^b is computed using the following polynomial approximation. |
| * (C. Hastings, Jr, 1955). |
| * |
| * __7__ |
| * \ |
| * \ |
| * 2^(-x) = / Ci*x^i |
| * /____ |
| * i=1 |
| * |
| * for x in the range 0.0 to 1.0 |
| * |
| * C0 = 1.0 |
| * C1 = -0.9999999995 |
| * C2 = 0.4999999206 |
| * C3 = -0.1666653019 |
| * C4 = 0.0416573475 |
| * C5 = -0.0083013598 |
| * C6 = 0.0013298820 |
| * C7 = -0.0001413161 |
| * |
| */ |
| static __inline vector float _exp2f4(vector float x) |
| { |
| vector signed int ix; |
| vector unsigned int overflow, underflow; |
| vector float frac, frac2, frac4; |
| vector float exp_int, exp_frac; |
| vector float result; |
| vector float hi, lo; |
| |
| vector float bias; |
| /* Break in the input x into two parts ceil(x), x - ceil(x). |
| */ |
| bias = (vector float)(spu_rlmaska((vector signed int)(x), -31)); |
| bias = (vector float)(spu_andc(spu_splats((unsigned int)0x3F7FFFFF), (vector unsigned int)bias)); |
| ix = spu_convts(spu_add(x, bias), 0); |
| frac = spu_sub(spu_convtf(ix, 0), x); |
| frac = spu_mul(frac, spu_splats((float)SM_LN2)); |
| |
| overflow = spu_rlmask(spu_cmpgt(ix, 128), -1); |
| underflow = spu_cmpgt(ix, -128); |
| |
| exp_int = (vector float)spu_and((vector unsigned int)spu_sl(spu_add(ix, 127), 23), underflow); |
| |
| /* Instruction counts can be reduced if the polynomial was |
| * computed entirely from nested (dependent) fma's. However, |
| * to reduce the number of pipeline stalls, the polygon is evaluated |
| * in two halves (hi amd lo). |
| */ |
| frac2 = spu_mul(frac, frac); |
| frac4 = spu_mul(frac2, frac2); |
| |
| hi = spu_madd(frac, spu_splats(-0.0001413161f), spu_splats(0.0013298820f)); |
| hi = spu_madd(frac, hi, spu_splats(-0.0083013598f)); |
| hi = spu_madd(frac, hi, spu_splats(0.0416573475f)); |
| lo = spu_madd(frac, spu_splats(-0.1666653019f), spu_splats(0.4999999206f)); |
| lo = spu_madd(frac, lo, spu_splats(-0.9999999995f)); |
| lo = spu_madd(frac, lo, spu_splats(1.0f)); |
| |
| exp_frac = spu_madd(frac4, hi, lo); |
| ix = spu_add(ix, spu_rlmask((vector signed int)(exp_frac), -23)); |
| result = spu_mul(exp_frac, exp_int); |
| |
| /* Handle overflow */ |
| result = spu_or(result, (vector float)overflow); |
| |
| return (result); |
| |
| } |
| |
| #endif /* _EXP2F4_H_ */ |
| #endif /* __SPU__ */ |