diff options
| -rw-r--r-- | generic/tclStrToD.c | 39 | ||||
| -rw-r--r-- | tests/expr.test | 4 |
2 files changed, 35 insertions, 8 deletions
diff --git a/generic/tclStrToD.c b/generic/tclStrToD.c index 883e2ea..c1b3e99 100644 --- a/generic/tclStrToD.c +++ b/generic/tclStrToD.c @@ -1548,7 +1548,7 @@ MakeLowPrecisionDouble( * Test for the easy cases. */ - if (numSigDigs <= DBL_DIG) { + if (numSigDigs <= QUICK_MAX) { if (exponent >= 0) { if (exponent <= mmaxpow) { /* @@ -1561,7 +1561,7 @@ MakeLowPrecisionDouble( ((Tcl_WideInt)significand * pow10vals[exponent]); goto returnValue; } else { - int diff = DBL_DIG - numSigDigs; + int diff = QUICK_MAX - numSigDigs; if (exponent-diff <= mmaxpow) { /* @@ -1798,6 +1798,12 @@ RefineApproximation( double quot; /* Correction term. */ double minincr; /* Lower bound on the absolute value of the * correction term. */ + int roundToEven; /* Flag == TRUE if we need to invoke + * "round to even" functionality */ + double rteSignificand; /* Significand of the round-to-even result */ + int rteExponent; /* Exponent of the round-to-even result */ + Tcl_WideInt rteSigWide; /* Wide integer version of the significand + * for testing evenness */ int i; /* @@ -1893,17 +1899,34 @@ RefineApproximation( mp_div_2d(&twoMv, -multiplier, &twoMv, NULL); } - /* - * If the result is less than unity, the error is less than 1/2 unit in - * the last place, so there's no correction to make. - */ - - if (mp_cmp_mag(&twoMd, &twoMv) == MP_LT) { + switch (mp_cmp_mag(&twoMd, &twoMv)) { + case MP_LT: + /* + * If the result is less than unity, the error is less than 1/2 unit in + * the last place, so there's no correction to make. + */ mp_clear(&twoMd); mp_clear(&twoMv); return approxResult; + case MP_EQ: + /* + * If the result is exactly unity, we need to round to even. + */ + roundToEven = 1; + break; + case MP_GT: + roundToEven = 0; + break; } + if (roundToEven) { + rteSignificand = frexp(approxResult, &rteExponent); + rteSigWide = (Tcl_WideInt) ldexp(rteSignificand, FP_PRECISION); + if ((rteSigWide & 1) == 0) { + return approxResult; + } + } + /* * Convert the numerator and denominator of the corrector term accurately * to floating point numbers. diff --git a/tests/expr.test b/tests/expr.test index 6ad7208..4c03262 100644 --- a/tests/expr.test +++ b/tests/expr.test @@ -7174,6 +7174,10 @@ test expr-50.1 {test sqrt() of bignums with non-Inf answer} { expr {sqrt("1[string repeat 0 616]") == 1e308} } 1 +test expr-51.1 {test round-to-even on input} { + expr 6.9294956446009195e15 +} 6929495644600920.0 + # cleanup |