what is happening with this assembly language Function Code (00401000) Comment arg_0 = byte ptr 8 Parameter p

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what is happening with this assembly language
Function Code (00401000)
Comment
arg_0 =byte ptr 8
Parameter passed to function, one byte
push ebp
Function prolog
mov ebp, esp
Function prolog
movzx eax, [ebp+arg_0]
cmp eax, 61h
jl short loc_401034
movzx ecx, [ebp+arg_0]
cmp ecx, 7Ah
jg short loc_401034
movzx edx, [ebp+arg_0]
add edx, 0Dh
mov [ebp+arg_0], dl
movzx eax, [ebp+arg_0]
cmp eax, 7Ah
jle short loc_401032
movzx ecx, [ebp+arg_0]
sub ecx, 1Ah
mov [ebp+arg_0], cl
loc_401032:
jmp short loc_401063
loc_401034:
movzx edx, [ebp+arg_0]
cmp edx, 41h
jl short loc_401063
movzx eax, [ebp+arg_0]
cmp eax, 5Ah
jg short loc_401063
movzx ecx, [ebp+arg_0]
add ecx, 0Dh
mov [ebp+arg_0], cl
movzx eax, [ebp+arg_0]
cmp eax, 5Ah
jle short loc_401063
movzx eax, [ebp+arg_0]
sub eax, 1Ah
mov [ebp+arg_0], al
loc_401063:
mov al, [ebp+arg_0]
pop ebp
Function Epilog etc
main function 401070
Comments
var_28 = dword ptr -28h
var_24 = dword ptr -24h
var_20 = dword ptr -20h
var_4 = dword ptr -4
var_4 stores random number used for stack canary
push ebp
mov ebp, esp
Prolog
sub esp, 28h
Room on stack for local variables
mov eax, dword_413020
xor eax, ebp
Stores random value to be used for stack canary
push esi
push edi
mov ecx, 6
mov esi, offset aUggcJjj_onqthl
lea edi, [ebp+var_20]
repmovsd
movsw
movsb
mov [ebp+var_28], 0
mov [ebp+var_24], 0
mov [ebp+var_28], 1Bh
mov [ebp+var_24],0
jmp short loc_4010BB
loc_4010B2:
mov eax, [ebp+var_24
add eax,1
mov [ebp+var_24], eax
loc_4010BB
mov ecx, [ebp+var_24]
cmp ecx, [ebp+var_28]
jnb short loc_4010DD
mov edx, [ebp+var_24]
movzx eax, byte ptr [ebp+edx+var_20
push eax
call sub_401000
add esp,4
mov ecx, [ebp+var_24]
mov byte ptr [ebp+ecx+var_20], al
jmp short loc_4010B2