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Diffstat (limited to 'docs/assembly.rst')
| -rw-r--r-- | docs/assembly.rst | 13 |
1 files changed, 11 insertions, 2 deletions
diff --git a/docs/assembly.rst b/docs/assembly.rst index 5041e72c..91ba076a 100644 --- a/docs/assembly.rst +++ b/docs/assembly.rst @@ -609,12 +609,21 @@ first. Solidity manages memory in a very simple way: There is a "free memory pointer" at position ``0x40`` in memory. If you want to allocate memory, just use the memory -from that point on and update the pointer accordingly. +starting from where this pointer points at and update it accordingly. +There is no built-in mechanism to release or free allocated memory. +Here is an assembly snippet that can be used for allocating memory:: + + function allocate(length) -> pos { + pos := mload(0x40) + mstore(0x40, add(pos, length)) + } The first 64 bytes of memory can be used as "scratch space" for short-term allocation. The 32 bytes after the free memory pointer (i.e. starting at ``0x60``) is meant to be zero permanently and is used as the initial value for empty dynamic memory arrays. +This means that the allocatable memory starts at ``0x80``, which is the initial value +of the free memory pointer. Elements in memory arrays in Solidity always occupy multiples of 32 bytes (yes, this is even true for ``byte[]``, but not for ``bytes`` and ``string``). Multi-dimensional memory @@ -698,7 +707,7 @@ We consider the runtime bytecode of the following Solidity program:: The following assembly will be generated:: { - mstore(0x40, 0x60) // store the "free memory pointer" + mstore(0x40, 0x80) // store the "free memory pointer" // function dispatcher switch div(calldataload(0), exp(2, 226)) case 0xb3de648b { |