On Sun, 24 Jul 2022 15:45:17 GMT, Raffaello Giulietti <d...@openjdk.org> wrote:
>> I didn't test this variant, will do tomorrow when also reviewing the tests
>> themselves.
>
> The correct variant below passes the tests.
>
>
> // For binary16 subnormals, beside forcing exp to -15,
> // retain the difference expdelta = E_min - exp.
> // This is the excess shift value, in addition to 13, to be used
> // in the computations below.
> // Further the (hidden) msb with value 1 in f must be involved as
> well.
> int expdelta = 0;
> int msb = 0x0000_0000;
> if (exp < -14) {
> expdelta = -14 - exp;
> exp = -15;
> msb = 0x0080_0000;
> }
> int f_signif_bits = doppel & 0x007f_ffff | msb;
>
> // Significand bits as if using rounding to zero (truncation).
> short signif_bits = (short)(f_signif_bits >> (13 + expdelta));
>
> // For round to nearest even, determining whether or
> // not to round up (in magnitude) is a function of the
> // least significant bit (LSB), the next bit position
> // (the round position), and the sticky bit (whether
> // there are any nonzero bits in the exact result to
> // the right of the round digit). An increment occurs
> // in three cases:
> //
> // LSB Round Sticky
> // 0 1 1
> // 1 1 0
> // 1 1 1
> // See "Computer Arithmetic Algorithms," Koren, Table 4.9
>
> int lsb = f_signif_bits & (1 << 13 + expdelta);
> int round = f_signif_bits & (1 << 12 + expdelta);
> int sticky = f_signif_bits & ((1 << 12 + expdelta) - 1);
>
> if (round != 0 && ((lsb | sticky) != 0 )) {
> signif_bits++;
> }
>
> // No bits set in significand beyond the *first* exponent
> // bit, not just the sigificand; quantity is added to the
> // exponent to implement a carry out from rounding the
> // significand.
> assert (0xf800 & signif_bits) == 0x0;
>
> return (short)(sign_bit | ( ((exp + 15) << 10) + signif_bits ) );
Test classes look good.
-------------
PR: https://git.openjdk.org/jdk/pull/9422
