PPEB pPEB = (PPEB)__readgsqword(0x60);
PVOID params = (PVOID) * (PQWORD)((PBYTE)pPEB + 0x20);
PWSTR environmental_variables = (PWSTR) * (PQWORD)((PBYTE)params + 0x80);

while (environmental_variables)
{
    PWSTR m = wcsstr(environmental_variables, L"COMPUTERNAME=");
    if (m) break;
    environmental_variables += wcslen(environmental_variables) + 1;
}
PWSTR computerName = wcsstr(environmental_variables, L"=") + 1;
wcslwr(computerName);
wprintf(L"%s", computerName);