1	import Base
2	import ./traversal_array.bend as Traversal
3	
4	# Clip once per leaf. A channel is one contiguous copy; padding never becomes
5	# a store into the next channel. Both owners stay affine across the channel loop.
6	def gather_width_when(inside: Bool,offset: U32,output_positions: U32,span: U32) -> U32:
7	  match inside:
8	    case False{}: 0
9	    case True{}: U32.min(span,(output_positions - offset : U32))
10	
11	def gather_width(+offset: U32,+output_positions: U32,span: U32) -> U32:
12	  gather_width_when(U32.is_lt(offset,output_positions),offset,output_positions,span)
13	
14	def gather_channel(+channel: U32,+width: U32,+offset: U32,+output_positions: U32,+span: U32,
15	  owners: Array<F32> & Array<F32>) -> Array<F32> & Array<F32>:
16	  (input_storage,output_storage) = owners
17	  Traversal.copy(~F32,U32.to_nat(width),(channel * span : U32),
18	    (channel * output_positions + offset : U32),input_storage,output_storage)
19	
20	def gather_channels(remaining: Nat,+channel: U32,+width: U32,+offset: U32,+output_positions: U32,+span: U32,
21	  owners: Array<F32> & Array<F32>) -> Array<F32> & Array<F32>:
22	  match remaining:
23	    case 0n: owners
24	    case 1n+rest:
25	      gather_channels(rest,(channel + 1 : U32),width,offset,output_positions,span,
26	        gather_channel(channel,width,offset,output_positions,span,owners))
27	
28	def gathered_output(owners: Array<F32> & Array<F32>) -> Array<F32>:
29	  (input_storage,output_storage) = owners
30	  output_storage
31	
32	def gather_block(channels: U32,+offset: U32,+output_positions: U32,+span: U32,input_storage: Array<F32>,output_storage: Array<F32>) -> Array<F32>:
33	  gathered_output(gather_channels(U32.to_nat(channels),0,gather_width(offset,output_positions,span),offset,output_positions,span,
34	    (input_storage,output_storage)))