diff options
Diffstat (limited to 'Modules/_decimal/libmpdec')
| -rw-r--r-- | Modules/_decimal/libmpdec/mpdecimal.c | 26 |
1 files changed, 19 insertions, 7 deletions
diff --git a/Modules/_decimal/libmpdec/mpdecimal.c b/Modules/_decimal/libmpdec/mpdecimal.c index 346e5ee..4b76fcd 100644 --- a/Modules/_decimal/libmpdec/mpdecimal.c +++ b/Modules/_decimal/libmpdec/mpdecimal.c @@ -4632,14 +4632,26 @@ mpd_qln(mpd_t *result, const mpd_t *a, const mpd_context_t *ctx, _settriple(result, MPD_POS, 0, 0); return; } - /* Check if the result will overflow. + /* + * Check if the result will overflow (0 < x, x != 1): + * 1) log10(x) < 0 iff adjexp(x) < 0 + * 2) 0 < x /\ x <= y ==> adjexp(x) <= adjexp(y) + * 3) 0 < x /\ x != 1 ==> 2 * abs(log10(x)) < abs(log(x)) + * 4) adjexp(x) <= log10(x) < adjexp(x) + 1 * - * 1) adjexp(a) + 1 > log10(a) >= adjexp(a) + * Case adjexp(x) >= 0: + * 5) 2 * adjexp(x) < abs(log(x)) + * Case adjexp(x) > 0: + * 6) adjexp(2 * adjexp(x)) <= adjexp(abs(log(x))) + * Case adjexp(x) == 0: + * mpd_exp_digits(t)-1 == 0 <= emax (the shortcut is not triggered) * - * 2) |log10(a)| >= adjexp(a), if adjexp(a) >= 0 - * |log10(a)| > -adjexp(a)-1, if adjexp(a) < 0 - * - * 3) |log(a)| > 2*|log10(a)| + * Case adjexp(x) < 0: + * 7) 2 * (-adjexp(x) - 1) < abs(log(x)) + * Case adjexp(x) < -1: + * 8) adjexp(2 * (-adjexp(x) - 1)) <= adjexp(abs(log(x))) + * Case adjexp(x) == -1: + * mpd_exp_digits(t)-1 == 0 <= emax (the shortcut is not triggered) */ adjexp = mpd_adjexp(a); t = (adjexp < 0) ? -adjexp-1 : adjexp; @@ -4674,7 +4686,7 @@ mpd_qln(mpd_t *result, const mpd_t *a, const mpd_context_t *ctx, workctx.prec = prec; _mpd_qln(result, a, &workctx, status); _ssettriple(&ulp, MPD_POS, 1, - result->exp + result->digits-workctx.prec-1); + result->exp + result->digits-workctx.prec); workctx.prec = ctx->prec; mpd_qadd(&t1, result, &ulp, &workctx, &workctx.status); |