EIP-5656: MCOPY instruction

EIPs Core EIPs
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What do you mean by “memory expansion”?
AFAIK reading (MLOAD) from unwritten/uninitialized memory doesn’t expand it to the offset, only return the default value (0) which would fit your case

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you can do this today with CALLDATACOPY or CODECOPY, which do not by themselves trigger memory expansion

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any reference to a storage slot expands the memory. the user pays: Gmem * a + a^2 // 512 where “a” is the highest referenced slot (there’s a complex formula so that on each memory access that raises this total.
even MLOAD(highOffset) causes a memory expansion, and thus so is MCOPY.
so if you want to zero-out a block range by copying in zeroes from high offset, it will work, but cause a memory expansion.
So my suggestion was to define a certain very high offset as “always zero”, which means:

  • this memory range can’t be set with MSTORE/MCOPY
  • Referencing above this memory offset is always zero, and doesn’t cause memory expansion.
    The value itself should be high enough so it is infeasible to use it.
    e.g. 2**32 would cost 3*2**32 + (2**64/512), which obviously is out-of-gas
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