Hello. As further part of implementing roundeven is inlining, I was studying machine descriptions and I have a few questions.
As suggested, builtin functions provided a strong model for implementing roundeven. Keeping that in mind, I tried to inspect how similar functions (round/ceil) would get inlined. As it is dependent on target machine, (mine is i7, so should be x86_64 ? I wonder why gcc/config/ does not have x86_64 or amd64 directory. Or is it i386 itself as extended?), should *.s file after compilation contain the specific instruction if supported? I was unable to see such kind of instruction on any -O level. Different pattern names are available for machine descriptions <https://gcc.gnu.org/onlinedocs/gccint/Standard-Names.html>, also for round, ceil, etc. Will I have to add such pattern name for roundeven? (is it the same as optab defined in optabs.def?) Thanks, -Tejas On Thu, 13 Jun 2019 at 00:27, Tejas Joshi <tejasjoshi9...@gmail.com> wrote: > > Hello. > > > I don't think you should have the unreachable "return false;" in is_even. > > The last "else if" can just be "else". > > I don't think return false in is_even is unreachable. As per my > understanding, when one else if is true in the else if ladder, all the > subsequent "else ifs" including "else" are ignored. When REAL_EXP is > less than SIGNIFICAND_BITS, but the number is odd, the inner "if" for > even-odd will not return true in which case should return false. That > case will ignore next "else if" and will reach return false. > > > Suppose REAL_EXP (r) > SIGNIFICAND_BITS. Then the number is definitely > > even, so you should return true, not false. > > for this condition, else if can be modified to just else and return true. > PATCH: > > gcc/ChangeLog: > > 2019-06-12 Tejas Joshi <tejasjoshi9...@gmail.com> > > * builtins.c (mathfn_built_in_2): Added CASE_MATHFN for ROUNDEVEN. > * builtins.def: Added function definitions for roundeven function > variants. > * fold-const-call.c (fold_const_call_ss): Added case for function > call and fold_const_conversion call for roundeven function. > * fold-const.c (negate_mathfn_p): Added case for roundeven function. > (tree_call_nonnegative_warnv_p): Added case for roundeven function. > (integer_valued_real_call_p): Added case for roundeven function. > * real.c (is_even): New function. Returns true if real number is > even, otherwise returns false. > (is_halfway_below): New function. Returns true if real number is > halfway between two integers, else return false. > (real_roundeven): New function. Round real number to nearest > integer, rounding halfway cases towards even. > * real.h (real_value): Added descriptive comments. > Added function declaration for roundeven function. > > gcc/testsuite/ChangeLog: > > 2019-06-12 Tejas Joshi <tejasjoshi9...@gmail.com> > > * gcc.dg/torture/builtin-round-roundeven.c: New test. > * gcc.dg/torture/builtin-round-roundevenf128.c: New test. > > > > On Tue, 11 Jun 2019 at 01:56, Joseph Myers <jos...@codesourcery.com> wrote: > > > > On Sun, 9 Jun 2019, Tejas Joshi wrote: > > > > > Hello. > > > I have created another patch which addresses the above points, > > > attached herewith. > > > > I don't think you should have the unreachable "return false;" in is_even. > > The last "else if" can just be "else". > > > > > > a conditional with < not <=; if REAL_EXP (r) == SIGNIFICAND_BITS, the > > > > least significant bit has value 1 and the number must be an integer). > > > > > > The number is integer because of the whole word spaces is occupied by > > > integer part? > > > Also, why would the least significant bit will have value 1 if > > > REAL_EXP (r) == SIGNIFICAND_BITS, as it only concerns with 2^0th > > > position (even or odd)? > > > > My understanding is that the significand is, as per the comments in > > real.c, in the range [0.5, 1.0). There are SIGNIFICAND_BITS bits. The > > bit above the most significant one has value 2^REAL_EXP. The most > > significant one has value 2^(REAL_EXP-1). The least significant one has > > value 2^(REAL_EXP-SIGNIFICAND_BITS). If REAL_EXP == SIGNIFICAND_BITS, > > that means the least significant bit has value 2^0 = 1, and there are no > > bits with value 0.5 or below, so the number is an integer. > > > > -- > > Joseph S. Myers > > jos...@codesourcery.com
