pub mod vm
# ===== SYSTEM PROCEDURES ==========================================================================
#! Removes elements deep in the stack until the depth of the stack is exactly 16. The elements
#! are removed in such a way that the top 16 elements of the stack remain unchanged. If the stack
#! would otherwise contain more than 16 elements at the end of execution, then adding a call to this
#! function at the end will reduce the size of the public inputs that are shared with the verifier.
#!
#! Input: Stack with 16 or more elements.
#! Output: Stack with only the original top 16 elements.
#!
#! Cycles: 17 + 11 * overflow_words, where `overflow_words` is the number of words needed to drop.
@locals(4)
pub proc truncate_stack()
# save the first word to memory and bring elements to be dropped to the top of the stack
loc_storew_le.0 dropw movupw.3
# => [X, B, C, D, ...]
# until stack depth greater than 16, keep dropping extra elements
sdepth neq.16
while.true
dropw movupw.3
# => [X, B, C, D, ...]
sdepth neq.16
end
# => [X, B, C, D, ...]
# bring the previously saved word back onto the stack
loc_loadw_le.0
# => [A, B, C, D, ...]
end
#! Drop 16 values from the stack.
pub proc drop_stack_top()
dropw dropw dropw dropw
end