On Mon, Aug 19, 2019 at 04:42:16PM -0500, Paul A. Clarke wrote: > From: "Paul A. Clarke" > > helper_todouble() was not properly converting any denormalized 32 bit > float to 64 bit double. > > Fix-suggested-by: Richard Henderson > Signed-off-by: Paul A. Clarke > > v2: > - Splitting patch "ppc: Three floating point fixes"; this is just one part. > - Original suggested "fix" was likely flawed. v2 is rewritten by > Richard Henderson (Thanks, Richard!); I reformatted the comments in a > couple of places, compiled, and tested. Applied to ppc-for-4.2, thanks. > --- > target/ppc/fpu_helper.c | 17 +++++++++++++---- > 1 file changed, 13 insertions(+), 4 deletions(-) > > diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c > index 52bcda2..07bc905 100644 > --- a/target/ppc/fpu_helper.c > +++ b/target/ppc/fpu_helper.c > @@ -73,11 +73,20 @@ uint64_t helper_todouble(uint32_t arg) > /* Zero or Denormalized operand. */ > ret = (uint64_t)extract32(arg, 31, 1) << 63; > if (unlikely(abs_arg != 0)) { > - /* Denormalized operand. */ > - int shift = clz32(abs_arg) - 9; > - int exp = -126 - shift + 1023; > + /* > + * Denormalized operand. > + * Shift fraction so that the msb is in the implicit bit position. > + * Thus, shift is in the range [1:23]. > + */ > + int shift = clz32(abs_arg) - 8; > + /* > + * The first 3 terms compute the float64 exponent. We then bias > + * this result by -1 so that we can swallow the implicit bit below. > + */ > + int exp = -126 - shift + 1023 - 1; > + > ret |= (uint64_t)exp << 52; > - ret |= abs_arg << (shift + 29); > + ret += (uint64_t)abs_arg << (52 - 23 + shift); > } > } > return ret; -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson