By extending the set of floating types, TS 18661-3 thereby affected the definition of DECIMAL_DIG, which is defined in terms of the "widest supported floating type". This is not conditional on whether __STDC_WANT_IEC_60559_TYPES_EXT__ is defined when <float.h> is included.
I raised this possible incompatibility with C11 (an implementation should be able to conform simultaneously with C11, and with C11 + TS 18661) in DR#501. This is not yet resolved, but the latest proposal <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2108.pdf> would obsolete DECIMAL_DIG with the intention of limiting it to the C11 types (so making it equivalent to LDBL_DECIMAL_DIG). (This proposal is intended to go along with a corresponding change to TS 18661-3 to avoid the new types and non-arithmetic interchange encodings affecting the value of DECIMAL_DIG.) To avoid releasing GCC 7 with a wider-than-C11 value of DECIMAL_DIG and possibly reverting back to a C11 value in a future release, this patch reverts back to the C11 value now. If the proposed resolution to DR#501 changes again so that DECIMAL_DIG *should* have a wider-than-C11 value, we can move back to a wider-than-C11 value in GCC 8. Bootstrapped with no regressions on x86_64-pc-linux-gnu. Applied to mainline. gcc/c-family: 2017-02-17 Joseph Myers <jos...@codesourcery.com> * c-cppbuiltin.c (builtin_define_float_constants): Define __DECIMAL_DIG__ to the value for long double. gcc/testsuite: 2017-02-17 Joseph Myers <jos...@codesourcery.com> * gcc.dg/c11-float-2.c: New test. * gcc.dg/torture/float128-floath.c, gcc.dg/torture/float128x-floath.c, gcc.dg/torture/float16-floath.c, gcc.dg/torture/float32-floath.c, gcc.dg/torture/float32x-floath.c, gcc.dg/torture/float64-floath.c, gcc.dg/torture/float64x-floath.c: Do not test comparison of *_DECIMAL_DIG macros with DECIMAL_DIG. Index: gcc/c-family/c-cppbuiltin.c =================================================================== --- gcc/c-family/c-cppbuiltin.c (revision 245538) +++ gcc/c-family/c-cppbuiltin.c (working copy) @@ -245,11 +245,10 @@ builtin_define_float_constants (const char *name_p if (type_decimal_dig < type_d_decimal_dig) type_decimal_dig++; } - /* Arbitrarily, define __DECIMAL_DIG__ when defining macros for long - double, although it may be greater than the value for long - double. */ + /* Define __DECIMAL_DIG__ to the value for long double to be + compatible with C99 and C11; see DR#501 and N2108. */ if (type == long_double_type_node) - builtin_define_with_int_value ("__DECIMAL_DIG__", decimal_dig); + builtin_define_with_int_value ("__DECIMAL_DIG__", type_decimal_dig); sprintf (name, "__%s_DECIMAL_DIG__", name_prefix); builtin_define_with_int_value (name, type_decimal_dig); Index: gcc/testsuite/gcc.dg/c11-float-2.c =================================================================== --- gcc/testsuite/gcc.dg/c11-float-2.c (nonexistent) +++ gcc/testsuite/gcc.dg/c11-float-2.c (working copy) @@ -0,0 +1,9 @@ +/* Test DECIMAL_DIG equals LDBL_DECIMAL_DIG; see DR#501 and N2108. */ +/* { dg-do preprocess } */ +/* { dg-options "-std=c11 -pedantic-errors" } */ + +#include <float.h> + +#if DECIMAL_DIG != LDBL_DECIMAL_DIG +# error "DECIMAL_DIG != LDBL_DECIMAL_DIG" +#endif Index: gcc/testsuite/gcc.dg/torture/float128-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float128-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float128-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT128_TRUE_MIN undefined" #endif -#if FLT128_DECIMAL_DIG > DECIMAL_DIG -# error "FLT128_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT128_MANT_DIG != 113 || FLT128_MAX_EXP != 16384 || FLT128_MIN_EXP != -16381 # error "_Float128 bad format" #endif Index: gcc/testsuite/gcc.dg/torture/float128x-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float128x-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float128x-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT128X_TRUE_MIN undefined" #endif -#if FLT128X_DECIMAL_DIG > DECIMAL_DIG -# error "FLT128X_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT128X_MANT_DIG < 128 || FLT128X_MAX_EXP < 65536 || FLT128X_MIN_EXP + FLT128X_MAX_EXP != 3 # error "_Float128x bad format" #endif Index: gcc/testsuite/gcc.dg/torture/float16-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float16-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float16-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT16_TRUE_MIN undefined" #endif -#if FLT16_DECIMAL_DIG > DECIMAL_DIG -# error "FLT16_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT16_MANT_DIG != 11 || FLT16_MAX_EXP != 16 || FLT16_MIN_EXP != -13 # error "_Float16 bad format" #endif Index: gcc/testsuite/gcc.dg/torture/float32-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float32-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float32-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT32_TRUE_MIN undefined" #endif -#if FLT32_DECIMAL_DIG > DECIMAL_DIG -# error "FLT32_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT32_MANT_DIG != 24 || FLT32_MAX_EXP != 128 || FLT32_MIN_EXP != -125 # error "_Float32 bad format" #endif Index: gcc/testsuite/gcc.dg/torture/float32x-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float32x-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float32x-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT32X_TRUE_MIN undefined" #endif -#if FLT32X_DECIMAL_DIG > DECIMAL_DIG -# error "FLT32X_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT32X_MANT_DIG < 32 || FLT32X_MAX_EXP < 1024 || FLT32X_MIN_EXP + FLT32X_MAX_EXP != 3 # error "_Float32x bad format" #endif Index: gcc/testsuite/gcc.dg/torture/float64-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float64-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float64-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT64_TRUE_MIN undefined" #endif -#if FLT64_DECIMAL_DIG > DECIMAL_DIG -# error "FLT64_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT64_MANT_DIG != 53 || FLT64_MAX_EXP != 1024 || FLT64_MIN_EXP != -1021 # error "_Float64 bad format" #endif Index: gcc/testsuite/gcc.dg/torture/float64x-floath.c =================================================================== --- gcc/testsuite/gcc.dg/torture/float64x-floath.c (revision 245538) +++ gcc/testsuite/gcc.dg/torture/float64x-floath.c (working copy) @@ -53,10 +53,6 @@ # error "FLT64X_TRUE_MIN undefined" #endif -#if FLT64X_DECIMAL_DIG > DECIMAL_DIG -# error "FLT64X_DECIMAL_DIG > DECIMAL_DIG" -#endif - #if FLT64X_MANT_DIG < 64 || FLT64X_MAX_EXP < 16384 || FLT64X_MIN_EXP + FLT64X_MAX_EXP != 3 # error "_Float64x bad format" #endif -- Joseph S. Myers jos...@codesourcery.com