Commit c0e6616b authored by Paul A. Clarke's avatar Paul A. Clarke Committed by David Gibson
Browse files

ppc: Fix emulated single to double denormalized conversions 



helper_todouble() was not properly converting any denormalized 32 bit
float to 64 bit double.

Fix-suggested-by: default avatarRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: default avatarPaul A. Clarke <pc@us.ibm.com>

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.
Message-Id: <1566250936-14538-1-git-send-email-pc@us.ibm.com>

Signed-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
parent a7b7b983

target/ppc/fpu_helper.c

+13 −4
Original line number Diff line number Diff line
@@ -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;