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39 /* -------------------------------------------------------------- */
40 /* PROLOG END TAG zYx */
41 #ifdef __SPU__
42 #ifndef _RECIPF4_H_
43 #define _RECIPF4_H_ 1
44
45 #include <spu_intrinsics.h>
46
47 /*
48 * FUNCTION
49 * vector float _recipf4(vector float value)
50 *
51 * DESCRIPTION
52 * The _recipf4 function inverts the vector "value" and returns the
53 * result.
54 *
55 */
_recipf4(vector float a)56 static __inline vector float _recipf4(vector float a)
57 {
58 /* This function has been designed to provide a
59 * full function operation that presisely computes
60 * the reciprocal for the entire range of extended
61 * single precision input <a>. This includes:
62 *
63 * 1) Computing the reciprocal to full single precision
64 * floating point accuracy.
65 * 2) Round the result consistently with the rounding
66 * mode of the processor - truncated toward zero.
67 * 3) Underflow and overflow results are clamped to
68 * Smin and Smax and flagged with the appropriate
69 * UNF or OVF exception in the FPSCR.
70 * 4) Divide By Zero (DBZ) exception is produced when
71 * the input <a> has a zero exponent. A reciprocal
72 * of correctly signed Smax is produced.
73 * 5) Resulting denorm reciprocal will be coerced to +0.
74 * 6) If a non-compliant IEEE result is produced, the
75 * a DIFF exception is generated.
76 */
77 vector float err, x0, x1;
78 vector float mult;
79 vector float mant_a;
80 vector float one = spu_splats(1.0f);
81 vector unsigned int exp, exp_a;
82 vector unsigned int exp_mask = (vec_uint4)spu_splats(0x7F800000);
83
84 /* If a has a zero exponent, then set the divide by zero
85 * (DBZ) exception flag. The estimate result is discarded.
86 */
87 (void)si_frest((qword)(a));
88
89 /* For computing the reciprocal, force the value
90 * into the range (1.0 <= 0 < 2.0).
91 */
92 mant_a = spu_sel(a, one, exp_mask);
93
94 /* Compute the reciprocal using the reciprocal estimate
95 * followed by one iteration of the Newton-Raphson.
96 * Due to truncation error, the quotient result may be low
97 * by 1 ulp (unit of least position). Conditionally add one
98 * if the estimate is too small.
99 */
100 x0 = spu_re(mant_a);
101 x0 = spu_madd(spu_nmsub(mant_a, x0, one), x0, x0);
102
103 x1 = (vector float)(spu_add((vector unsigned int)(x0), 1));
104 err = spu_nmsub(mant_a, x1, one);
105
106 x1 = spu_sel(x0, x1, spu_cmpgt((vector signed int)(err), -1));
107
108 /* Compute the reciprocal's expected exponent. If the exponent
109 * is out of range, then force the resulting exponent to 0.
110 * (127 with the bias). We correct for the out of range
111 * values by computing a multiplier (mult) that will force the
112 * result to the correct out of range value and set the
113 * correct exception flag (UNF, OVF, or neither). The multiplier
114 * is also conditioned to generate correctly signed Smax if the
115 * inoput <a> is a denorm or zero.
116 */
117 exp_a = spu_and((vector unsigned int)a, exp_mask);
118 exp = spu_add(spu_sub(spu_splats((unsigned int)0x7F000000), exp_a), spu_cmpabsgt(mant_a, one));
119
120 /* The default multiplier is 1.0. If an underflow is detected (ie,
121 * either the dividend <a> is a denorm/zero, or the computed exponent is
122 * less than or equal to a biased 0), force the multiplier to 0.0.
123 */
124 mult = spu_and(one, (vector float)spu_cmpgt((vector signed int)(exp), 0));
125
126 /* Force the multiplier to positive Smax (0x7FFFFFFF) and the biased exponent
127 * to 127, if the divisor is denorm/zero or the computed biased exponent is
128 * greater than 255.
129 */
130 mult = spu_or(mult, (vector float)spu_rlmask(spu_cmpeq(exp_a, 0), -1));
131
132 /* Insert the exponent into the result and perform the
133 * final multiplication.
134 */
135 x1 = spu_sel(x1, (vector float)exp, exp_mask);
136 x1 = spu_mul(x1, mult);
137
138 return (x1);
139 }
140
141 #endif /* _RECIPF4_H_ */
142 #endif /* __SPU__ */
143
