ReverseSequence

# Given this:
 batch_dim = 0
 seq_dim = 1
 input.dims = (4, 8, ...)
 seq_lengths = [7, 2, 3, 5]
 
 # then slices of input are reversed on seq_dim, but only up to seq_lengths:
 output[0, 0:7, :, ...] = input[0, 7:0:-1, :, ...]
 output[1, 0:2, :, ...] = input[1, 2:0:-1, :, ...]
 output[2, 0:3, :, ...] = input[2, 3:0:-1, :, ...]
 output[3, 0:5, :, ...] = input[3, 5:0:-1, :, ...]
 
 # while entries past seq_lens are copied through:
 output[0, 7:, :, ...] = input[0, 7:, :, ...]
 output[1, 2:, :, ...] = input[1, 2:, :, ...]
 output[2, 3:, :, ...] = input[2, 3:, :, ...]
 output[3, 2:, :, ...] = input[3, 2:, :, ...]
 

# Given this:
 batch_dim = 2
 seq_dim = 0
 input.dims = (8, ?, 4, ...)
 seq_lengths = [7, 2, 3, 5]
 
 # then slices of input are reversed on seq_dim, but only up to seq_lengths:
 output[0:7, :, 0, :, ...] = input[7:0:-1, :, 0, :, ...]
 output[0:2, :, 1, :, ...] = input[2:0:-1, :, 1, :, ...]
 output[0:3, :, 2, :, ...] = input[3:0:-1, :, 2, :, ...]
 output[0:5, :, 3, :, ...] = input[5:0:-1, :, 3, :, ...]
 
 # while entries past seq_lens are copied through:
 output[7:, :, 0, :, ...] = input[7:, :, 0, :, ...]
 output[2:, :, 1, :, ...] = input[2:, :, 1, :, ...]
 output[3:, :, 2, :, ...] = input[3:, :, 2, :, ...]
 output[2:, :, 3, :, ...] = input[2:, :, 3, :, ...]