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(expand_float): When converting an unsigned type U to a smaller or equal-sized floating type F where there's no hardware support for unsigned-to-float conversion... 

(expand_float): When converting an unsigned type U
to a smaller or equal-sized floating type F where there's no
hardware support for unsigned-to-float conversion, use a temporary
floating type larger than F if possible, since this avoids
rounding problems that are worst when U is just greater than
the maximum signed integer of the same size.

From-SVN: r3778
This commit is contained in:
Paul Eggert 1993-03-18 21:28:43 +00:00
parent 0cdd3dddae
commit c95c47f3e9
1 changed files with 20 additions and 4 deletions
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24
gcc/optabs.c
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@ -3572,11 +3572,27 @@ expand_float (to, from, unsignedp)
if (flag_force_mem)
from = force_not_mem (from);
/* Look for a usable floating mode FMODE wider than the source and at
least as wide as the target. Using FMODE will avoid rounding woes
with unsigned values greater than the signed maximum value. */
for (fmode = GET_MODE (to); fmode != VOIDmode;
fmode = GET_MODE_WIDER_MODE (fmode))
if (GET_MODE_BITSIZE (GET_MODE (from)) < GET_MODE_BITSIZE (fmode)
&& can_float_p (fmode, GET_MODE (from), 0) != CODE_FOR_nothing)
break;
if (fmode == VOIDmode)
{
/* There is no such mode. Pretend the target is wide enough.
This may cause rounding problems, unfortunately. */
fmode = GET_MODE (to);
}
/* If we are about to do some arithmetic to correct for an
unsigned operand, do it in a pseudo-register. */
if (GET_CODE (to) != REG || REGNO (to) <= LAST_VIRTUAL_REGISTER)
target = gen_reg_rtx (GET_MODE (to));
if (GET_MODE (to) != fmode
|| GET_CODE (to) != REG || REGNO (to) <= LAST_VIRTUAL_REGISTER)
target = gen_reg_rtx (fmode);
/* Convert as signed integer to floating. */
expand_float (target, from, 0);
@ -3591,8 +3607,8 @@ expand_float (to, from, unsignedp)
Rather than setting up a dconst_dot_5, let's hope SCO
fixes the bug. */
offset = REAL_VALUE_LDEXP (dconst1, GET_MODE_BITSIZE (GET_MODE (from)));
temp = expand_binop (GET_MODE (to), add_optab, target,
immed_real_const_1 (offset, GET_MODE (to)),
temp = expand_binop (fmode, add_optab, target,
immed_real_const_1 (offset, fmode),
target, 0, OPTAB_LIB_WIDEN);
if (temp != target)
emit_move_insn (target, temp);