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Diffstat (limited to 'gcc-4.4.3/gcc/ada/exp_pakd.ads')
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diff --git a/gcc-4.4.3/gcc/ada/exp_pakd.ads b/gcc-4.4.3/gcc/ada/exp_pakd.ads deleted file mode 100644 index 0c2e815e2..000000000 --- a/gcc-4.4.3/gcc/ada/exp_pakd.ads +++ /dev/null @@ -1,275 +0,0 @@ ------------------------------------------------------------------------------- --- -- --- GNAT COMPILER COMPONENTS -- --- -- --- E X P _ P A K D -- --- -- --- S p e c -- --- -- --- Copyright (C) 1992-2008, Free Software Foundation, Inc. -- --- -- --- GNAT is free software; you can redistribute it and/or modify it under -- --- terms of the GNU General Public License as published by the Free Soft- -- --- ware Foundation; either version 3, or (at your option) any later ver- -- --- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- --- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- --- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- --- for more details. You should have received a copy of the GNU General -- --- Public License distributed with GNAT; see file COPYING3. If not, go to -- --- http://www.gnu.org/licenses for a complete copy of the license. -- --- -- --- GNAT was originally developed by the GNAT team at New York University. -- --- Extensive contributions were provided by Ada Core Technologies Inc. -- --- -- ------------------------------------------------------------------------------- - --- Expand routines for manipulation of packed arrays - -with Types; use Types; - -package Exp_Pakd is - - ------------------------------------- - -- Implementation of Packed Arrays -- - ------------------------------------- - - -- When a packed array (sub)type is frozen, we create a corresponding - -- type that will be used to hold the bits of the packed value, and - -- store the entity for this type in the Packed_Array_Type field of the - -- E_Array_Type or E_Array_Subtype entity for the packed array. - - -- This packed array type has the name xxxPn, where xxx is the name - -- of the packed type, and n is the component size. The expanded - -- declaration declares a type that is one of the following: - - -- For an unconstrained array with component size 1,2,4 or any other - -- odd component size. These are the cases in which we do not need - -- to align the underlying array. - - -- type xxxPn is new Packed_Bytes1; - - -- For an unconstrained array with component size that is divisible - -- by 2, but not divisible by 4 (other than 2 itself). These are the - -- cases in which we can generate better code if the underlying array - -- is 2-byte aligned (see System.Pack_14 in file s-pack14 for example). - - -- type xxxPn is new Packed_Bytes2; - - -- For an unconstrained array with component size that is divisible - -- by 4, other than powers of 2 (which either come under the 1,2,4 - -- exception above, or are not packed at all). These are cases where - -- we can generate better code if the underlying array is 4-byte - -- aligned (see System.Pack_20 in file s-pack20 for example). - - -- type xxxPn is new Packed_Bytes4; - - -- For a constrained array with a static index type where the number - -- of bits does not exceed the size of Unsigned: - - -- type xxxPn is new Unsigned range 0 .. 2 ** nbits - 1; - - -- For a constrained array with a static index type where the number - -- of bits is greater than the size of Unsigned, but does not exceed - -- the size of Long_Long_Unsigned: - - -- type xxxPn is new Long_Long_Unsigned range 0 .. 2 ** nbits - 1; - - -- For all other constrained arrays, we use one of - - -- type xxxPn is new Packed_Bytes1 (0 .. m); - -- type xxxPn is new Packed_Bytes2 (0 .. m); - -- type xxxPn is new Packed_Bytes4 (0 .. m); - - -- where m is calculated (from the length of the original packed array) - -- to hold the required number of bits, and the choice of the particular - -- Packed_Bytes{1,2,4} type is made on the basis of alignment needs as - -- described above for the unconstrained case. - - -- When a variable of packed array type is allocated, gigi will allocate - -- the amount of space indicated by the corresponding packed array type. - -- However, we do NOT attempt to rewrite the types of any references or - -- to retype the variable itself, since this would cause all kinds of - -- semantic problems in the front end (remember that expansion proceeds - -- at the same time as analysis). - - -- For an indexed reference to a packed array, we simply convert the - -- reference to the appropriate equivalent reference to the object - -- of the packed array type (using unchecked conversion). - - -- In some cases (for internally generated types, and for the subtypes - -- for record fields that depend on a discriminant), the corresponding - -- packed type cannot be easily generated in advance. In these cases, - -- we generate the required subtype on the fly at the reference point. - - -- For the modular case, any unused bits are initialized to zero, and - -- all operations maintain these bits as zero (where necessary all - -- unchecked conversions from corresponding array values require - -- these bits to be clear, which is done automatically by gigi). - - -- For the array cases, there can be unused bits in the last byte, and - -- these are neither initialized, nor treated specially in operations - -- (i.e. it is allowable for these bits to be clobbered, e.g. by not). - - --------------------------- - -- Endian Considerations -- - --------------------------- - - -- The standard does not specify the way in which bits are numbered in - -- a packed array. There are two reasonable rules for deciding this: - - -- Store the first bit at right end (low order) word. This means - -- that the scaled subscript can be used directly as a left shift - -- count (if we put bit 0 at the left end, then we need an extra - -- subtract to compute the shift count). - - -- Layout the bits so that if the packed boolean array is overlaid on - -- a record, using unchecked conversion, then bit 0 of the array is - -- the same as the bit numbered bit 0 in a record representation - -- clause applying to the record. For example: - - -- type Rec is record - -- C : Bits4; - -- D : Bits7; - -- E : Bits5; - -- end record; - - -- for Rec use record - -- C at 0 range 0 .. 3; - -- D at 0 range 4 .. 10; - -- E at 0 range 11 .. 15; - -- end record; - - -- type P16 is array (0 .. 15) of Boolean; - -- pragma Pack (P16); - - -- Now if we use unchecked conversion to convert a value of the record - -- type to the packed array type, according to this second criterion, - -- we would expect field D to occupy bits 4..10 of the Boolean array. - - -- Although not required, this correspondence seems a highly desirable - -- property, and is one that GNAT decides to guarantee. For a little - -- endian machine, we can also meet the first requirement, but for a - -- big endian machine, it will be necessary to store the first bit of - -- a Boolean array in the left end (most significant) bit of the word. - -- This may cost an extra instruction on some machines, but we consider - -- that a worthwhile price to pay for the consistency. - - -- One more important point arises in the case where we have a constrained - -- subtype of an unconstrained array. Take the case of 20 bits. For the - -- unconstrained representation, we would use an array of bytes: - - -- Little-endian case - -- 8-7-6-5-4-3-2-1 16-15-14-13-12-11-10-9 x-x-x-x-20-19-18-17 - - -- Big-endian case - -- 1-2-3-4-5-6-7-8 9-10-11-12-13-14-15-16 17-18-19-20-x-x-x-x - - -- For the constrained case, we use a 20-bit modular value, but in - -- general this value may well be stored in 32 bits. Let's look at - -- what it looks like: - - -- Little-endian case - - -- x-x-x-x-x-x-x-x-x-x-x-x-20-19-18-17-...-10-9-8-7-6-5-4-3-2-1 - - -- which stored in memory looks like - - -- 8-7-...-2-1 16-15-...-10-9 x-x-x-x-20-19-18-17 x-x-x-x-x-x-x - - -- An important rule is that the constrained and unconstrained cases - -- must have the same bit representation in memory, since we will often - -- convert from one to the other (e.g. when calling a procedure whose - -- formal is unconstrained). As we see, that criterion is met for the - -- little-endian case above. Now let's look at the big-endian case: - - -- Big-endian case - - -- x-x-x-x-x-x-x-x-x-x-x-x-1-2-3-4-5-6-7-8-9-10-...-17-18-19-20 - - -- which stored in memory looks like - - -- x-x-x-x-x-x-x-x x-x-x-x-1-2-3-4 5-6-...11-12 13-14-...-19-20 - - -- That won't do, the representation value in memory is NOT the same in - -- the constrained and unconstrained case. The solution is to store the - -- modular value left-justified: - - -- 1-2-3-4-5-6-7-8-9-10-...-17-18-19-20-x-x-x-x-x-x-x-x-x-x-x - - -- which stored in memory looks like - - -- 1-2-...-7-8 9-10-...15-16 17-18-19-20-x-x-x-x x-x-x-x-x-x-x-x - - -- and now, we do indeed have the same representation for the memory - -- version in the constrained and unconstrained cases. - - ----------------- - -- Subprograms -- - ----------------- - - procedure Create_Packed_Array_Type (Typ : Entity_Id); - -- Typ is a array type or subtype to which pragma Pack applies. If the - -- Packed_Array_Type field of Typ is already set, then the call has no - -- effect, otherwise a suitable type or subtype is created and stored - -- in the Packed_Array_Type field of Typ. This created type is an Itype - -- so that Gigi will simply elaborate and freeze the type on first use - -- (which is typically the definition of the corresponding array type). - -- - -- Note: although this routine is included in the expander package for - -- packed types, it is actually called unconditionally from Freeze, - -- whether or not expansion (and code generation) is enabled. We do this - -- since we want gigi to be able to properly compute type characteristics - -- (for the Data Decomposition Annex of ASIS, and possible other future - -- uses) even if code generation is not active. Strictly this means that - -- this procedure is not part of the expander, but it seems appropriate - -- to keep it together with the other expansion routines that have to do - -- with packed array types. - - procedure Expand_Packed_Boolean_Operator (N : Node_Id); - -- N is an N_Op_And, N_Op_Or or N_Op_Xor node whose operand type is a - -- packed boolean array. This routine expands the appropriate operations - -- to carry out the logical operation on the packed arrays. It handles - -- both the modular and array representation cases. - - procedure Expand_Packed_Element_Reference (N : Node_Id); - -- N is an N_Indexed_Component node whose prefix is a packed array. In - -- the bit packed case, this routine can only be used for the expression - -- evaluation case, not the assignment case, since the result is not a - -- variable. See Expand_Bit_Packed_Element_Set for how the assignment case - -- is handled in the bit packed case. For the enumeration case, the result - -- of this call is always a variable, so the call can be used for both the - -- expression evaluation and assignment cases. - - procedure Expand_Bit_Packed_Element_Set (N : Node_Id); - -- N is an N_Assignment_Statement node whose name is an indexed - -- component of a bit-packed array. This procedure rewrites the entire - -- assignment statement with appropriate code to set the referenced - -- bits of the packed array type object. Note that this procedure is - -- used only for the bit-packed case, not for the enumeration case. - - procedure Expand_Packed_Eq (N : Node_Id); - -- N is an N_Op_Eq node where the operands are packed arrays whose - -- representation is an array-of-bytes type (the case where a modular - -- type is used for the representation does not require any special - -- handling, because in the modular case, unused bits are zeroes. - - procedure Expand_Packed_Not (N : Node_Id); - -- N is an N_Op_Not node where the operand is packed array of Boolean - -- in standard representation (i.e. component size is one bit). This - -- procedure expands the corresponding not operation. Note that the - -- non-standard representation case is handled by using a loop through - -- elements generated by the normal non-packed circuitry. - - function Involves_Packed_Array_Reference (N : Node_Id) return Boolean; - -- N is the node for a name. This function returns true if the name - -- involves a packed array reference. A node involves a packed array - -- reference if it is itself an indexed component referring to a bit- - -- packed array, or it is a selected component whose prefix involves - -- a packed array reference. - - procedure Expand_Packed_Address_Reference (N : Node_Id); - -- The node N is an attribute reference for the 'Address reference, where - -- the prefix involves a packed array reference. This routine expands the - -- necessary code for performing the address reference in this case. - -end Exp_Pakd; |