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7dbbb6dde3
are workarounds for various symptoms of the problem described in clang bugs 3929, 8100, 8241, 10409, and 12958. The regression tests did their job: they failed, someone brought it up on the mailing lists, and then the issue got ignored for 6 months. Oops. There may still be some regressions for functions we don't have test coverage for yet.
82 lines
2.4 KiB
C
82 lines
2.4 KiB
C
/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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/*
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* Float version of e_log2.c. See the latter for most comments.
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*/
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#include "math.h"
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#include "math_private.h"
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#include "k_logf.h"
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static const float
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two25 = 3.3554432000e+07, /* 0x4c000000 */
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ivln2hi = 1.4428710938e+00, /* 0x3fb8b000 */
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ivln2lo = -1.7605285393e-04; /* 0xb9389ad4 */
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static const float zero = 0.0;
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static volatile float vzero = 0.0;
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float
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__ieee754_log2f(float x)
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{
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float f,hfsq,hi,lo,r,y;
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int32_t i,k,hx;
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GET_FLOAT_WORD(hx,x);
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k=0;
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if (hx < 0x00800000) { /* x < 2**-126 */
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if ((hx&0x7fffffff)==0)
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return -two25/vzero; /* log(+-0)=-inf */
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if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
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k -= 25; x *= two25; /* subnormal number, scale up x */
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GET_FLOAT_WORD(hx,x);
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}
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if (hx >= 0x7f800000) return x+x;
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if (hx == 0x3f800000)
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return zero; /* log(1) = +0 */
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k += (hx>>23)-127;
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hx &= 0x007fffff;
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i = (hx+(0x4afb0d))&0x800000;
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SET_FLOAT_WORD(x,hx|(i^0x3f800000)); /* normalize x or x/2 */
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k += (i>>23);
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y = (float)k;
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f = x - (float)1.0;
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hfsq = (float)0.5*f*f;
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r = k_log1pf(f);
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/*
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* We no longer need to avoid falling into the multi-precision
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* calculations due to compiler bugs breaking Dekker's theorem.
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* Keep avoiding this as an optimization. See e_log2.c for more
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* details (some details are here only because the optimization
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* is not yet available in double precision).
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*
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* Another compiler bug turned up. With gcc on i386,
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* (ivln2lo + ivln2hi) would be evaluated in float precision
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* despite runtime evaluations using double precision. So we
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* must cast one of its terms to float_t. This makes the whole
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* expression have type float_t, so return is forced to waste
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* time clobbering its extra precision.
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*/
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if (sizeof(float_t) > sizeof(float))
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return (r - hfsq + f) * ((float_t)ivln2lo + ivln2hi) + y;
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hi = f - hfsq;
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GET_FLOAT_WORD(hx,hi);
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SET_FLOAT_WORD(hi,hx&0xfffff000);
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lo = (f - hi) - hfsq + r;
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return (lo+hi)*ivln2lo + lo*ivln2hi + hi*ivln2hi + y;
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}
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