| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNAT RUN-TIME COMPONENTS -- |
| -- -- |
| -- S Y S T E M . B I T F I E L D _ U T I L S -- |
| -- -- |
| -- B o d y -- |
| -- -- |
| -- Copyright (C) 2019-2021, 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. -- |
| -- -- |
| -- As a special exception under Section 7 of GPL version 3, you are granted -- |
| -- additional permissions described in the GCC Runtime Library Exception, -- |
| -- version 3.1, as published by the Free Software Foundation. -- |
| -- -- |
| -- You should have received a copy of the GNU General Public License and -- |
| -- a copy of the GCC Runtime Library Exception along with this program; -- |
| -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- |
| -- <http://www.gnu.org/licenses/>. -- |
| -- -- |
| -- GNAT was originally developed by the GNAT team at New York University. -- |
| -- Extensive contributions were provided by Ada Core Technologies Inc. -- |
| -- -- |
| ------------------------------------------------------------------------------ |
| |
| package body System.Bitfield_Utils is |
| |
| package body G is |
| |
| Val_Bytes : constant Address := Address (Val'Size / Storage_Unit); |
| |
| -- A Val_2 can cross a memory page boundary (e.g. an 8-byte Val_2 that |
| -- starts 4 bytes before the end of a page). If the bit field also |
| -- crosses that boundary, then the second page is known to exist, and we |
| -- can safely load or store the Val_2. On the other hand, if the bit |
| -- field is entirely within the first half of the Val_2, then it is |
| -- possible (albeit highly unlikely) that the second page does not |
| -- exist, so we must load or store only the first half of the Val_2. |
| -- Get_Val_2 and Set_Val_2 take care of all this. |
| |
| function Get_Val_2 |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset; |
| Size : Small_Size) |
| return Val_2; |
| -- Get the Val_2, taking care to only load the first half when |
| -- necessary. |
| |
| procedure Set_Val_2 |
| (Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| V : Val_2; |
| Size : Small_Size); |
| -- Set the Val_2, taking care to only store the first half when |
| -- necessary. |
| |
| -- Get_Bitfield and Set_Bitfield are helper functions that get/set small |
| -- bit fields -- the value fits in Val, and the bit field is placed |
| -- starting at some offset within the first half of a Val_2. |
| -- Copy_Bitfield, on the other hand, supports arbitrarily large bit |
| -- fields. All operations require bit offsets to point within the first |
| -- Val pointed to by the address. |
| |
| function Get_Bitfield |
| (Src : Val_2; Src_Offset : Bit_Offset; Size : Small_Size) |
| return Val with Inline; |
| -- Returns the bit field in Src starting at Src_Offset, of the given |
| -- Size. If Size < Small_Size'Last, then high order bits are zero. |
| |
| function Set_Bitfield |
| (Src_Value : Val; |
| Dest : Val_2; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size) |
| return Val_2 with Inline; |
| -- The bit field in Dest starting at Dest_Offset, of the given Size, is |
| -- set to Src_Value. Src_Value must have high order bits (Size and |
| -- above) zero. The result is returned as the function result. |
| |
| procedure Set_Bitfield |
| (Src_Value : Val; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size); |
| -- This version takes the bit address and size of the destination. |
| |
| procedure Copy_Small_Bitfield |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size); |
| -- Copy_Bitfield in the case where Size <= Val'Size. |
| -- The Address values must be aligned as for Val and Val_2. |
| -- This works for overlapping bit fields. |
| |
| procedure Copy_Large_Bitfield |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| Size : Bit_Size); |
| -- Copy_Bitfield in the case where Size > Val'Size. |
| -- The Address values must be aligned as for Val and Val_2. |
| -- This works for overlapping bit fields only if the source |
| -- bit address is greater than or equal to the destination |
| -- bit address, because it copies forward (from lower to higher |
| -- bit addresses). |
| |
| function Get_Val_2 |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset; |
| Size : Small_Size) |
| return Val_2 is |
| begin |
| pragma Assert (Src_Address mod Val'Alignment = 0); |
| |
| -- Bit field fits in first half; fetch just one Val. On little |
| -- endian, we want that in the low half, but on big endian, we |
| -- want it in the high half. |
| |
| if Src_Offset + Size <= Val'Size then |
| declare |
| Result : aliased constant Val with |
| Import, Address => Src_Address; |
| begin |
| return (case Endian is |
| when Little => Val_2 (Result), |
| when Big => Shift_Left (Val_2 (Result), Val'Size)); |
| end; |
| |
| -- Bit field crosses into the second half, so it's safe to fetch the |
| -- whole Val_2. |
| |
| else |
| declare |
| Result : aliased constant Val_2 with |
| Import, Address => Src_Address; |
| begin |
| return Result; |
| end; |
| end if; |
| end Get_Val_2; |
| |
| procedure Set_Val_2 |
| (Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| V : Val_2; |
| Size : Small_Size) is |
| begin |
| pragma Assert (Dest_Address mod Val'Alignment = 0); |
| |
| -- Comments in Get_Val_2 apply, except we're storing instead of |
| -- fetching. |
| |
| if Dest_Offset + Size <= Val'Size then |
| declare |
| Dest : aliased Val with Import, Address => Dest_Address; |
| begin |
| Dest := (case Endian is |
| when Little => Val'Mod (V), |
| when Big => Val (Shift_Right (V, Val'Size))); |
| end; |
| else |
| declare |
| Dest : aliased Val_2 with Import, Address => Dest_Address; |
| begin |
| Dest := V; |
| end; |
| end if; |
| end Set_Val_2; |
| |
| function Get_Bitfield |
| (Src : Val_2; Src_Offset : Bit_Offset; Size : Small_Size) |
| return Val |
| is |
| L_Shift_Amount : constant Natural := |
| (case Endian is |
| when Little => Val_2'Size - (Src_Offset + Size), |
| when Big => Src_Offset); |
| Temp1 : constant Val_2 := |
| Shift_Left (Src, L_Shift_Amount); |
| Temp2 : constant Val_2 := |
| Shift_Right (Temp1, Val_2'Size - Size); |
| begin |
| return Val (Temp2); |
| end Get_Bitfield; |
| |
| function Set_Bitfield |
| (Src_Value : Val; |
| Dest : Val_2; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size) |
| return Val_2 |
| is |
| pragma Assert (Size = Val'Size or else Src_Value < 2**Size); |
| L_Shift_Amount : constant Natural := |
| (case Endian is |
| when Little => Dest_Offset, |
| when Big => Val_2'Size - (Dest_Offset + Size)); |
| Mask : constant Val_2 := |
| Shift_Left (Shift_Left (1, Size) - 1, L_Shift_Amount); |
| Temp1 : constant Val_2 := Dest and not Mask; |
| Temp2 : constant Val_2 := |
| Shift_Left (Val_2 (Src_Value), L_Shift_Amount); |
| Result : constant Val_2 := Temp1 or Temp2; |
| begin |
| return Result; |
| end Set_Bitfield; |
| |
| procedure Set_Bitfield |
| (Src_Value : Val; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size) |
| is |
| Old_Dest : constant Val_2 := |
| Get_Val_2 (Dest_Address, Dest_Offset, Size); |
| New_Dest : constant Val_2 := |
| Set_Bitfield (Src_Value, Old_Dest, Dest_Offset, Size); |
| begin |
| Set_Val_2 (Dest_Address, Dest_Offset, New_Dest, Size); |
| end Set_Bitfield; |
| |
| procedure Copy_Small_Bitfield |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size) |
| is |
| Src : constant Val_2 := Get_Val_2 (Src_Address, Src_Offset, Size); |
| V : constant Val := Get_Bitfield (Src, Src_Offset, Size); |
| begin |
| Set_Bitfield (V, Dest_Address, Dest_Offset, Size); |
| end Copy_Small_Bitfield; |
| |
| -- Copy_Large_Bitfield does the main work. Copying aligned Vals is more |
| -- efficient than fiddling with shifting and whatnot. But we can't align |
| -- both source and destination. We choose to align the destination, |
| -- because that's more efficient -- Set_Bitfield needs to read, then |
| -- modify, then write, whereas Get_Bitfield does not. |
| -- |
| -- So the method is: |
| -- |
| -- Step 1: |
| -- If the destination is not already aligned, copy Initial_Size |
| -- bits, and increment the bit addresses. Initial_Size is chosen to |
| -- be the smallest size that will cause the destination bit address |
| -- to be aligned (i.e. have zero bit offset from the already-aligned |
| -- Address). Get_Bitfield and Set_Bitfield are used here. |
| -- |
| -- Step 2: |
| -- Loop, copying Vals. Get_Bitfield is used to fetch a Val-sized |
| -- bit field, but Set_Bitfield is not needed -- we can set the |
| -- aligned Val with an array indexing. |
| -- |
| -- Step 3: |
| -- Copy remaining smaller-than-Val bits, if any |
| |
| procedure Copy_Large_Bitfield |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset; |
| Size : Bit_Size) |
| is |
| Sz : Bit_Size := Size; |
| S_Addr : Address := Src_Address; |
| S_Off : Bit_Offset := Src_Offset; |
| D_Addr : Address := Dest_Address; |
| D_Off : Bit_Offset := Dest_Offset; |
| begin |
| if S_Addr < D_Addr or else (S_Addr = D_Addr and then S_Off < D_Off) |
| then |
| -- Here, the source bit address is less than the destination bit |
| -- address. Assert that there is no overlap. |
| |
| declare |
| Temp_Off : constant Bit_Offset'Base := S_Off + Size; |
| After_S_Addr : constant Address := |
| S_Addr + Address (Temp_Off / Storage_Unit); |
| After_S_Off : constant Bit_Offset_In_Byte := |
| Temp_Off mod Storage_Unit; |
| -- (After_S_Addr, After_S_Off) is the bit address of the bit |
| -- just after the source bit field. Assert that it's less than |
| -- or equal to the destination bit address. |
| Overlap_OK : constant Boolean := |
| After_S_Addr < D_Addr |
| or else |
| (After_S_Addr = D_Addr and then After_S_Off <= D_Off); |
| begin |
| pragma Assert (Overlap_OK); |
| end; |
| end if; |
| |
| if D_Off /= 0 then |
| -- Step 1: |
| |
| declare |
| Initial_Size : constant Small_Size := Val'Size - D_Off; |
| Initial_Val_2 : constant Val_2 := |
| Get_Val_2 (S_Addr, S_Off, Initial_Size); |
| Initial_Val : constant Val := |
| Get_Bitfield (Initial_Val_2, S_Off, Initial_Size); |
| |
| begin |
| Set_Bitfield |
| (Initial_Val, D_Addr, D_Off, Initial_Size); |
| |
| Sz := Sz - Initial_Size; |
| declare |
| New_S_Off : constant Bit_Offset'Base := S_Off + Initial_Size; |
| begin |
| if New_S_Off > Bit_Offset'Last then |
| S_Addr := S_Addr + Val_Bytes; |
| S_Off := New_S_Off - Small_Size'Last; |
| else |
| S_Off := New_S_Off; |
| end if; |
| end; |
| D_Addr := D_Addr + Val_Bytes; |
| pragma Assert (D_Off + Initial_Size = Val'Size); |
| D_Off := 0; |
| end; |
| end if; |
| |
| -- Step 2: |
| |
| declare |
| Dest_Arr : Val_Array (1 .. Sz / Val'Size) with Import, |
| Address => D_Addr; |
| begin |
| for Dest_Comp of Dest_Arr loop |
| declare |
| pragma Warnings (Off); |
| pragma Assert (Dest_Comp in Val); |
| pragma Warnings (On); |
| pragma Assert (Dest_Comp'Valid); |
| Src_V_2 : constant Val_2 := |
| Get_Val_2 (S_Addr, S_Off, Val'Size); |
| Full_V : constant Val := |
| Get_Bitfield (Src_V_2, S_Off, Val'Size); |
| begin |
| Dest_Comp := Full_V; |
| S_Addr := S_Addr + Val_Bytes; |
| -- S_Off remains the same |
| end; |
| end loop; |
| |
| Sz := Sz mod Val'Size; |
| if Sz /= 0 then |
| -- Step 3: |
| |
| declare |
| Final_Val_2 : constant Val_2 := |
| Get_Val_2 (S_Addr, S_Off, Sz); |
| Final_Val : constant Val := |
| Get_Bitfield (Final_Val_2, S_Off, Sz); |
| begin |
| Set_Bitfield |
| (Final_Val, D_Addr + Dest_Arr'Length * Val_Bytes, 0, Sz); |
| end; |
| end if; |
| end; |
| end Copy_Large_Bitfield; |
| |
| procedure Copy_Bitfield |
| (Src_Address : Address; |
| Src_Offset : Bit_Offset_In_Byte; |
| Dest_Address : Address; |
| Dest_Offset : Bit_Offset_In_Byte; |
| Size : Bit_Size) |
| is |
| -- Align the Address values as for Val and Val_2, and adjust the |
| -- Bit_Offsets accordingly. |
| |
| Src_Adjust : constant Address := Src_Address mod Val_Bytes; |
| Al_Src_Address : constant Address := Src_Address - Src_Adjust; |
| Al_Src_Offset : constant Bit_Offset := |
| Src_Offset + Bit_Offset (Src_Adjust * Storage_Unit); |
| |
| Dest_Adjust : constant Address := Dest_Address mod Val_Bytes; |
| Al_Dest_Address : constant Address := Dest_Address - Dest_Adjust; |
| Al_Dest_Offset : constant Bit_Offset := |
| Dest_Offset + Bit_Offset (Dest_Adjust * Storage_Unit); |
| |
| pragma Assert (Al_Src_Address mod Val'Alignment = 0); |
| pragma Assert (Al_Dest_Address mod Val'Alignment = 0); |
| begin |
| -- Optimized small case |
| |
| if Size in Small_Size then |
| Copy_Small_Bitfield |
| (Al_Src_Address, Al_Src_Offset, |
| Al_Dest_Address, Al_Dest_Offset, |
| Size); |
| |
| -- Do nothing for zero size. This is necessary to avoid doing invalid |
| -- reads, which are detected by valgrind. |
| |
| elsif Size = 0 then |
| null; |
| |
| -- Large case |
| |
| else |
| Copy_Large_Bitfield |
| (Al_Src_Address, Al_Src_Offset, |
| Al_Dest_Address, Al_Dest_Offset, |
| Size); |
| end if; |
| end Copy_Bitfield; |
| |
| function Fast_Copy_Bitfield |
| (Src : Val_2; |
| Src_Offset : Bit_Offset; |
| Dest : Val_2; |
| Dest_Offset : Bit_Offset; |
| Size : Small_Size) |
| return Val_2 is |
| Result : constant Val_2 := Set_Bitfield |
| (Get_Bitfield (Src, Src_Offset, Size), Dest, Dest_Offset, Size); |
| begin |
| -- No need to explicitly do nothing for zero size case, because Size |
| -- cannot be zero. |
| |
| return Result; |
| end Fast_Copy_Bitfield; |
| |
| end G; |
| |
| end System.Bitfield_Utils; |
