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Fix oflow bound in exp and pow. #604

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Dec 3, 2024
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Fix oflow bound in exp and pow. #604

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12 changes: 9 additions & 3 deletions src/common/misc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -13,10 +13,15 @@
#include <string.h>
#endif


#ifndef M_PI
#define M_PI 3.141592653589793238462643383279502884
#endif

#ifndef M_PIf
# define M_PIf ((float)M_PI)
#endif

#ifndef M_PIl
#define M_PIl 3.141592653589793238462643383279502884L
#endif
Expand Down Expand Up @@ -137,9 +142,10 @@
#define L2Lf 1.428606765330187045e-06f

#define R_LN2f 1.442695040888963407359924681001892137426645954152985934135449406931f
#ifndef M_PIf
# define M_PIf ((float)M_PI)
#endif

// Overflow bound for exp and pow

#define LOG_DBL_MAX 0x1.62e42fefa39efp+9 /* 709.782712893384 */

//

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4 changes: 4 additions & 0 deletions src/libm-tester/tester.c
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Expand Up @@ -3903,6 +3903,8 @@ void do_test() {
fprintf(stderr, "exp : ");
for(d = -10;d < 10 && success;d += 0.002) checkAccuracy_d(mpfr_exp, child_exp, d, 1.0);
for(d = -1000;d < 1000 && success;d += 1.1) checkAccuracy_d(mpfr_exp, child_exp, d, 1.0);
// Test for early or late overflow, e.g before or after x = LOG_DBL_MAX
for(d = LOG_DBL_MAX - 0.0001;(d < LOG_DBL_MAX + 0.0001) && success;d += 0.00001) checkAccuracy_d(mpfr_exp, child_exp, d, 1.0);
showResult(success);

//
Expand All @@ -3914,6 +3916,8 @@ void do_test() {
}
}
for(y = -1000;y < 1000 && success;y += 0.1) checkAccuracy_d_d(mpfr_pow, child_pow, 2.1, y, 1.0);
// Test for early or late overflow (test limited to x = e)
for(d = LOG_DBL_MAX - 0.0001;(d < LOG_DBL_MAX + 0.0001) && success;d += 0.00001) checkAccuracy_d_d(mpfr_pow, child_pow, exp(1.0), d, 1.0);
showResult(success);

//
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6 changes: 3 additions & 3 deletions src/libm/sleefdp.c
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Expand Up @@ -1490,9 +1490,9 @@ EXPORT CONST double xexp(double d) {
u = s * s * u + s + 1;
u = ldexp2k(u, q);

if (d > 709.78271114955742909217217426) u = SLEEF_INFINITY;
if (d > LOG_DBL_MAX) u = SLEEF_INFINITY;
if (d < -1000) u = 0;

return u;
}

Expand Down Expand Up @@ -1641,7 +1641,7 @@ EXPORT CONST double xpow(double x, double y) {
Sleef_double2 d = ddmul_d2_d2_d(logk(fabsk(x)), y);
double result = expk(d);

result = (d.x > 709.78271114955742909217217426 || xisnan(result)) ? SLEEF_INFINITY : result;
result = (d.x > LOG_DBL_MAX || xisnan(result)) ? SLEEF_INFINITY : result;
result *= (x > 0 ? 1 : (yisint ? (yisodd ? -1 : 1) : SLEEF_NAN));

double efx = mulsign(fabsk(x) - 1, y);
Expand Down
12 changes: 5 additions & 7 deletions src/libm/sleefsimddp.c
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Expand Up @@ -2167,10 +2167,11 @@ EXPORT CONST VECTOR_CC vdouble xexp(vdouble d) {

u = vadd_vd_vd_vd(vcast_vd_d(1), vmla_vd_vd_vd_vd(vmul_vd_vd_vd(s, s), u, s));
#endif // #ifdef ENABLE_FMA_DP

u = vldexp2_vd_vd_vi(u, q);

u = vsel_vd_vo_vd_vd(vgt_vo_vd_vd(d, vcast_vd_d(709.78271114955742909217217426)), vcast_vd_d(SLEEF_INFINITY), u);
vopmask o = vgt_vo_vd_vd(d, vcast_vd_d(LOG_DBL_MAX));
u = vsel_vd_vo_vd_vd(o, vcast_vd_d(SLEEF_INFINITY), u);
u = vreinterpret_vd_vm(vandnot_vm_vo64_vm(vlt_vo_vd_vd(d, vcast_vd_d(-1000)), vreinterpret_vm_vd(u)));

return u;
Expand Down Expand Up @@ -2340,13 +2341,13 @@ static INLINE CONST VECTOR_CC vdouble expk(vdouble2 d) {

#if !defined(DETERMINISTIC)
EXPORT CONST VECTOR_CC vdouble xpow(vdouble x, vdouble y) {
#if 1
vopmask yisint = visint_vo_vd(y);
vopmask yisodd = vand_vo_vo_vo(visodd_vo_vd(y), yisint);

vdouble2 d = ddmul_vd2_vd2_vd(logk(vabs_vd_vd(x)), y);
vdouble result = expk(d);
result = vsel_vd_vo_vd_vd(vgt_vo_vd_vd(vd2getx_vd_vd2(d), vcast_vd_d(709.78271114955742909217217426)), vcast_vd_d(SLEEF_INFINITY), result);
vopmask o = vgt_vo_vd_vd(vd2getx_vd_vd2(d), vcast_vd_d(LOG_DBL_MAX));
result = vsel_vd_vo_vd_vd(o, vcast_vd_d(SLEEF_INFINITY), result);

result = vmul_vd_vd_vd(result,
vsel_vd_vo_vd_vd(vgt_vo_vd_vd(x, vcast_vd_d(0)),
Expand All @@ -2372,9 +2373,6 @@ EXPORT CONST VECTOR_CC vdouble xpow(vdouble x, vdouble y) {
result = vsel_vd_vo_vd_vd(vor_vo_vo_vo(veq_vo_vd_vd(y, vcast_vd_d(0)), veq_vo_vd_vd(x, vcast_vd_d(1))), vcast_vd_d(1), result);

return result;
#else
return expk(ddmul_vd2_vd2_vd(logk(x), y));
#endif
}
#endif // #if !defined(DETERMINISTIC)

Expand Down