```# a "yield" version of the REMAP algorithm, for FFT Tukey-Cooley schedules
# original code for the FFT Tukey-Cooley schedul:
# https://www.nayuki.io/res/free-small-fft-in-multiple-languages/fft.py
"""
size = 2
while size <= n:
halfsize = size // 2
tablestep = n // size
for i in range(0, n, size):
k = 0
for j in range(i, i + halfsize):
jh = j+halfsize
jl = j
temp1 = vec[jh] * exptable[k]
temp2 = vec[jl]
vec[jh] = temp2 - temp1
vec[jl] = temp2 + temp1
k += tablestep
size *= 2
"""

# python "yield" can be iterated. use this to make it clear how
# the indices are generated by using natural-looking nested loops
def iterate_indices(SVSHAPE):
# get indices to iterate over, in the required order
n = SVSHAPE.lims[0]
# createing lists of indices to iterate over in each dimension
# has to be done dynamically, because it depends on the size
# first, the size-based loop (which can be done statically)
x_r = []
size = 2
while size <= n:
x_r.append(size)
size *= 2
# invert order if requested
if SVSHAPE.invxyz[0]: x_r.reverse()

if len(x_r) == 0:
return

# start an infinite (wrapping) loop
skip = 0
while True:
for size in x_r:           # loop over 3rd order dimension (size)
# y_r schedule depends on size
halfsize = size // 2
tablestep = n // size
y_r = []
for i in range(0, n, size):
y_r.append(i)
# invert if requested
if SVSHAPE.invxyz[1]: y_r.reverse()
for i in y_r:       # loop over 2nd order dimension
k_r = []
j_r = []
k = 0
for j in range(i, i+halfsize):
k_r.append(k)
j_r.append(j)
k += tablestep
# invert if requested
if SVSHAPE.invxyz[2]: k_r.reverse()
if SVSHAPE.invxyz[2]: j_r.reverse()
for j, k in zip(j_r, k_r):   # loop over 1st order dimension
# skip the first entries up to offset
if skip < SVSHAPE.offset:
skip += 1
continue
# now depending on MODE return the index
if SVSHAPE.skip == 0b00:
result = j              # for vec[j]
elif SVSHAPE.skip == 0b01:
result = j + halfsize   # for vec[j+halfsize]
elif SVSHAPE.skip == 0b10:
result = k              # for exptable[k]

yield result

def demo():
# set the dimension sizes here
xdim = 8
ydim = 0 # not needed
zdim = 0 # again, not needed

# set total. err don't know how to calculate how many there are...
# do it manually for now
VL = 0
size = 2
n = xdim
while size <= n:
halfsize = size // 2
tablestep = n // size
for i in range(0, n, size):
for j in range(i, i + halfsize):
VL += 1
size *= 2

# set up an SVSHAPE
class SVSHAPE:
pass
# j schedule
SVSHAPE0 = SVSHAPE()
SVSHAPE0.lims = [xdim, ydim, zdim]
SVSHAPE0.order = [0,1,2]  # experiment with different permutations, here
SVSHAPE0.mode = 0b01
SVSHAPE0.skip = 0b00
SVSHAPE0.offset = 0       # experiment with different offset, here
SVSHAPE0.invxyz = [0,0,0] # inversion if desired
# j+halfstep schedule
SVSHAPE1 = SVSHAPE()
SVSHAPE1.lims = [xdim, ydim, zdim]
SVSHAPE1.order = [0,1,2]  # experiment with different permutations, here
SVSHAPE1.mode = 0b01
SVSHAPE1.skip = 0b01
SVSHAPE1.offset = 0       # experiment with different offset, here
SVSHAPE1.invxyz = [0,0,0] # inversion if desired
# k schedule
SVSHAPE2 = SVSHAPE()
SVSHAPE2.lims = [xdim, ydim, zdim]
SVSHAPE2.order = [0,1,2]  # experiment with different permutations, here
SVSHAPE2.mode = 0b01
SVSHAPE2.skip = 0b10
SVSHAPE2.offset = 0       # experiment with different offset, here
SVSHAPE2.invxyz = [0,0,0] # inversion if desired

# enumerate over the iterator function, getting new indices
schedule = []
for idx, (jl, jh, k) in enumerate(zip(iterate_indices(SVSHAPE0),
iterate_indices(SVSHAPE1),
iterate_indices(SVSHAPE2))):
if idx >= VL:
break
schedule.append((jl, jh, k))

# ok now pretty-print the results, with some debug output
size = 2
idx = 0
while size <= n:
halfsize = size // 2
tablestep = n // size
print ("size %d halfsize %d tablestep %d" % \
(size, halfsize, tablestep))
for i in range(0, n, size):
prefix = "i %d\t" % i
k = 0
for j in range(i, i + halfsize):
jl, jh, ks = schedule[idx]
print ("  %-3d\t%s j=%-2d jh=%-2d k=%-2d -> "
"j[jl=%-2d] j[jh=%-2d] exptable[k=%d]" % \
(idx, prefix, j, j+halfsize, k,
jl, jh, ks))
k += tablestep
idx += 1
size *= 2

# run the demo
if __name__ == '__main__':
demo()
```