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From: Pierre-Marie de Rodat <pmderodat@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-1462] [Ada] Clarify the semantics of signed intrinsic shift operations Date: Tue, 15 Jun 2021 10:21:42 +0000 (GMT) [thread overview] Message-ID: <20210615102142.475B3398B168@sourceware.org> (raw) https://gcc.gnu.org/g:688fb8553bd589d6cfc71de467f38ae725199da9 commit r12-1462-g688fb8553bd589d6cfc71de467f38ae725199da9 Author: Yannick Moy <moy@adacore.com> Date: Fri Feb 5 15:19:57 2021 +0100 [Ada] Clarify the semantics of signed intrinsic shift operations gcc/ada/ * doc/gnat_rm/intrinsic_subprograms.rst: More details on shift operations for signed types. Also add the missing Import and Convention on the example. * gnat_rm.texi: Regenerate. Diff: --- gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst | 14 ++++++++------ gcc/ada/gnat_rm.texi | 14 ++++++++------ 2 files changed, 16 insertions(+), 12 deletions(-) diff --git a/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst b/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst index e448816572f..355b1399b2f 100644 --- a/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst +++ b/gcc/ada/doc/gnat_rm/intrinsic_subprograms.rst @@ -203,7 +203,8 @@ type (signed or modular), as in this example: function Shift_Left (Value : T; - Amount : Natural) return T; + Amount : Natural) return T + with Import, Convention => Intrinsic; The function name must be one of @@ -215,11 +216,12 @@ The result type must be the same as the type of ``Value``. The shift amount must be Natural. The formal parameter names can be anything. -A more convenient way of providing these shift operators is to use -the Provide_Shift_Operators pragma, which provides the function declarations -and corresponding pragma Import's for all five shift functions. Note that in -using these provided shift operations, shifts performed on negative numbers -will result in modification of the sign bit. +A more convenient way of providing these shift operators is to use the +Provide_Shift_Operators pragma, which provides the function declarations and +corresponding pragma Import's for all five shift functions. For signed types +the semantics of these operators is to interpret the bitwise result of the +corresponding operator for modular type. In particular, shifting a negative +number may change its sign bit to positive. .. _Source_Location: diff --git a/gcc/ada/gnat_rm.texi b/gcc/ada/gnat_rm.texi index 68729da05df..8f0a370f684 100644 --- a/gcc/ada/gnat_rm.texi +++ b/gcc/ada/gnat_rm.texi @@ -17917,7 +17917,8 @@ type (signed or modular), as in this example: @example function Shift_Left (Value : T; - Amount : Natural) return T; + Amount : Natural) return T +with Import, Convention => Intrinsic; @end example The function name must be one of @@ -17929,11 +17930,12 @@ The result type must be the same as the type of @code{Value}. The shift amount must be Natural. The formal parameter names can be anything. -A more convenient way of providing these shift operators is to use -the Provide_Shift_Operators pragma, which provides the function declarations -and corresponding pragma Import's for all five shift functions. Note that in -using these provided shift operations, shifts performed on negative numbers -will result in modification of the sign bit. +A more convenient way of providing these shift operators is to use the +Provide_Shift_Operators pragma, which provides the function declarations and +corresponding pragma Import's for all five shift functions. For signed types +the semantics of these operators is to interpret the bitwise result of the +corresponding operator for modular type. In particular, shifting a negative +number may change its sign bit to positive. @node Source_Location,,Shifts and Rotates,Intrinsic Subprograms @anchor{gnat_rm/intrinsic_subprograms source-location}@anchor{274}@anchor{gnat_rm/intrinsic_subprograms id13}@anchor{275}
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