Add binary search MASM example #160
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Thanks Denis! This is a super cool MASM program. I left a couple of comments in line.
One point: We try to use the convention now that we first write what the next line is about and then indicate the final stack after the operations / line with # => [...]
like here
# compute the pointer at which we should stop iterating
dup.1 add
# => [end_ptr, ptr, ...]
Can you change that quickly?
(I know it's not consistent yet with all the examples. I will change that.
We should combine this with the Bubble Sort of @phklive when merged.
examples/bsearch.masm
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| #! Binary searches for value `val` in the memory addresses range [start..end), sorted in ascending order. | ||
| #! | ||
| #! Input: [start, end, val, ...] | ||
| #! Output: [found (true/false), addr] where `found` is searching result (`true`/`false`), |
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where
foundis searching result (true/false)
nit: maybe better "where found indicates the result
examples/bsearch.masm
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| #! | ||
| #! Input: [start, end, val, ...] | ||
| #! Output: [found (true/false), addr] where `found` is searching result (`true`/`false`), | ||
| #! `addr` is an address of value (if it was found), or an address where value should be inserted. |
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addris an address of value (if it was found), or an address where value should be inserted.
nit: can you add address in memory?
examples/bsearch.masm
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| #! index `[0, count)` of `val`, if `val` was found; otherwise index in array, where `val` should be inserted. | ||
| proc.binary_search_stack | ||
| push.STARTING_MEMORY_ADDRESS # [STARTING_MEMORY_ADDRESS, count, arr[0], arr[1], ..., arr[count - 1], val, ...] | ||
| exec.read_stack_to_memory # [end, val, ...] |
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should it be write_stack_to_memort?
examples/bsearch.masm
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| #! | ||
| #! Input: [addr, count, arr[0], arr[1], ..., arr[count - 1], ...] | ||
| #! Output: [end, ...] where `end` is addr next vacant memory address, thus array occupies addresses `[addr..end)` in the memory | ||
| proc.read_stack_to_memory |
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same here, should it be write_stack_to_memory?
examples/bsearch.masm
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| #! Output: [end, ...] where `end` is addr next vacant memory address, thus array occupies addresses `[addr..end)` in the memory | ||
| proc.read_stack_to_memory | ||
| u32assert2 # [addr, count, arr[0], arr[1], ...] | ||
| dup.1 # [count, addr, c, arr[0], arr[1], ...] |
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nit: [count, addr, count, arr[0], arr[1], ...]
examples/bsearch.masm
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| if.true # [start, end, val, ...] | ||
| push.1 # [1, start, end, val, ...] | ||
| else # [start, end, val, ...] | ||
| # Push "not found" flag and flag to skip the loop |
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This would be an error, right?
You could use assert.err=123 and break.
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This is not an error. Binary searching is used not only for searching, but also for adding new values into a sorted array. In a case when value wasn't found, the algorithm must return an index where this value should be inserted.
examples/bsearch.masm
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| dup.1 # [end, start, end, val, ...] | ||
| dup.1 # [start, end, start, end, val, ...] | ||
| u32wrapping_sub # [count, start, end, val, ...], count = end - start | ||
| u32checked_div.2 # [count / 2, start, end, val, ...] |
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nit: can you add in the comment what happens if count is odd?
examples/bsearch.masm
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| swap # [start, middle, end, val, ...] | ||
| drop # [middle, end, val, ...] | ||
| # Prepare "found" flag and exit the loop | ||
| push.1.0 # [0, 1, addr, end, val, ...], addr = middle |
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I like the usage of the flags like this
examples/bsearch.masm
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| dup # [count, count, ...] | ||
| neq.0 # [count != 0, count, ...] | ||
| if.true # [count, arr[0], arr[1], ..., arr[count - 1], val, ...] | ||
| exec.binary_search_stack # [found, index] |
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can you maybe get rid of the found in the final output?
You could return all 0 if you didn't find the value and the pos of the stack if you found it
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I think, it wouldn't be a good idea to return indexes of the stack. We work with index in array, which is passed through the stack. If value is not found, index == 0 would conflict with the index of 0th element. I tried to use special index like 0xFFFFFFFF for such cases, but it made the code worse.
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agreed, thanks for the explanation
| swap # [found, index, ...] | ||
| end | ||
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| proc.test_empty |
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This is super nice that you made tests!
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Congrats for your first PR! |
This is a Miden Assembly example code, which performs binary search for a given value in a given ascending array. All input data should be provided in the
operands_stackof intputs-file. If theoperands_stackis empty, tests will run.