Tony Finch - tolower() in bulk at speed

visualize_tolower.py

# This is based on the post "2022-06-27 – tolower() in bulk at speed" by Tony Finch 
# link: https://dotat.at/@/2022-06-27-tolower-swar.html

## For me, it was quite hard to understand the post without some visual helps. So I made it.
## You can run this with python3 in terminal and I hope this would help you, too.

OCTETS = "ABSOLUTE"

def show_ascii(s):
    bins = bin(s)[2:].zfill(64)
    for i in range(0, 64, 8):
        print(chr(int(bins[i:i+8], 2)), end="")
    print()

OKGREEN = "\033[92m"
ENDC = "\033[0m"
def color(s):
    S = ""
    for ss in s:
        if (ss == "1"):
            S += OKGREEN + ss + ENDC
        else:
            S += ss
    return S

def show(s, memo=""):
    S = bin(s)[2:].zfill(64)
    S = str(S)

    for i in range(0, 8):
        print(color(S[i*8:i*8+8]), end=" ")
    print(color("   # " + memo))

def to_hex(s):
    return int(s.encode("utf-8").hex(), 16)    
    
all_bytes = 0x0101010101010101
octets = to_hex(OCTETS)

# show(all_bytes, "all_bytes")
show(octets, "octets")

steal_all_0x80 = 0x7F * all_bytes
show(steal_all_0x80, "0x7F * all_bytes")

heptets = octets & steal_all_0x80
show(heptets, "heptets = octets & (0x7F * all_bytes)")

print("-"*60)

# show(0x7F, "0x7F")
# show(to_hex('A'), "A")
# show(to_hex('Z'), "Z")

# print("-"*60)

is_gt_Z = heptets + (0x7F - to_hex('Z')) * all_bytes
show(is_gt_Z, "is_gt_Z = heptets + (0x7F - 'Z') * all_bytes -- (each first bit is true if heptet - 'Z' > 0)")

is_ge_A = heptets + (0x80 - to_hex('A')) * all_bytes
show(is_ge_A, "is_ge_A = heptets + (0x80 - 'A') * all_bytes -- (each first bit is true if heptet - 'A' >= 0)")
print(" -- above two example works only when the original char is btw 0 ~ 127 (ascii)")

print("-"*60)

is_ascii = (0xFF * all_bytes) ^ octets # ~octets make something not expected, so use other way
show(octets, "octets")
show(is_ascii, "is_ascii = ~octets -- (each first bit is true if it's ascii char)")

print("-"*60)

is_upper = is_ascii & (is_ge_A ^ is_gt_Z)
show(is_upper, "is_upper = is_ascii & (is_ge_A ^ is_gt_Z) -- (true only if is_ge_A=1 and is_gt_Z=0")
to_lower = (is_upper >> 2) & (0x20 * all_bytes)
show(to_lower, "to_lower = (is_upper >> 2) & (0x20 * all_bytes)")
# show(((is_ascii >> 2) & ((is_ge_A >> 2) ^ (is_gt_Z >> 2)) & (0x20 * all_bytes)), "same result")
show(octets, "octets")
result = octets | to_lower
show(result, "octets | to_lower")

print("-"*60)

show_ascii(result)

print("-"*60)

# another way
is_ascii = ~octets & (0x80 * all_bytes)
show(is_ascii, "is_ascii = ~octets & (0x80 * all_bytes)")
is_upper = is_ascii & (is_ge_A ^ is_gt_Z)
result = octets | is_upper >> 2
show(result, "octets | is_upper >> 2")

print("-"*60)

show_ascii(result) # same result

actually you don't even need to run it. Here's the output: