Convert native character string to ASCII array of integers

Given a string in the computer's native character set such as:

    "Hello"

, I want to convert it to an array of integers representing the ASCII
values of the characters. The reason I want to do this is that I'll be
passing the ASCII array to a cryptographic hash function. In order to
make my program fully ****table so that it will run properly on
machines where the default character set isn't ASCII, I've created a
MakeASCII function.

Please my MakeASCII function! Rip it apart!

typedef char unsigned OctetStorage;

void MakeASCII(OctetStorage *pos,char const *pc)
{
    for( ; ; ++pos,++pc)
    {
        switch (*pc)
        {
        case ' ': *pos = 0x20u; break;
        case '!': *pos = 0x21u; break;
        case '\"': *pos = 0x22u; break;
        case '#': *pos = 0x23u; break;
        case '$': *pos = 0x24u; break;
        case '%': *pos = 0x25u; break;
        case '&': *pos = 0x26u; break;
        case '\'': *pos = 0x27u; break;
        case '(': *pos = 0x28u; break;
        case ')': *pos = 0x29u; break;
        case '*': *pos = 0x2Au; break;
        case '+': *pos = 0x2Bu; break;
        case ',': *pos = 0x2Cu; break;
        case '-': *pos = 0x2Du; break;
        case '.': *pos = 0x2Eu; break;
        case '/': *pos = 0x2Fu; break;
        case '0': *pos = 0x30u; break;
        case '1': *pos = 0x31u; break;
        case '2': *pos = 0x32u; break;
        case '3': *pos = 0x33u; break;
        case '4': *pos = 0x34u; break;
        case '5': *pos = 0x35u; break;
        case '6': *pos = 0x36u; break;
        case '7': *pos = 0x37u; break;
        case '8': *pos = 0x38u; break;
        case '9': *pos = 0x39u; break;
        case ':': *pos = 0x3Au; break;
        case ';': *pos = 0x3Bu; break;
        case '<': *pos = 0x3Cu; break;
        case '=': *pos = 0x3Du; break;
        case '>': *pos = 0x3Eu; break;
        case '?': *pos = 0x3Fu; break;
        case '@[EMAIL PROTECTED]
': *pos = 0x40u; break;
        case 'A': *pos = 0x41u; break;
        case 'B': *pos = 0x42u; break;
        case 'C': *pos = 0x43u; break;
        case 'D': *pos = 0x44u; break;
        case 'E': *pos = 0x45u; break;
        case 'F': *pos = 0x46u; break;
        case 'G': *pos = 0x47u; break;
        case 'H': *pos = 0x48u; break;
        case 'I': *pos = 0x49u; break;
        case 'J': *pos = 0x4Au; break;
        case 'K': *pos = 0x4Bu; break;
        case 'L': *pos = 0x4Cu; break;
        case 'M': *pos = 0x4Du; break;
        case 'N': *pos = 0x4Eu; break;
        case 'O': *pos = 0x4Fu; break;
        case 'P': *pos = 0x50u; break;
        case 'Q': *pos = 0x51u; break;
        case 'R': *pos = 0x52u; break;
        case 'S': *pos = 0x53u; break;
        case 'T': *pos = 0x54u; break;
        case 'U': *pos = 0x55u; break;
        case 'V': *pos = 0x56u; break;
        case 'W': *pos = 0x57u; break;
        case 'X': *pos = 0x58u; break;
        case 'Y': *pos = 0x59u; break;
        case 'Z': *pos = 0x5Au; break;
        case '[': *pos = 0x5Bu; break;
        case '\\': *pos = 0x5Cu; break;
        case ']': *pos = 0x5Du; break;
        case '^': *pos = 0x5Eu; break;
        case '_': *pos = 0x5Fu; break;
        case '`': *pos = 0x60u; break;
        case 'a': *pos = 0x61u; break;
        case 'b': *pos = 0x62u; break;
        case 'c': *pos = 0x63u; break;
        case 'd': *pos = 0x64u; break;
        case 'e': *pos = 0x65u; break;
        case 'f': *pos = 0x66u; break;
        case 'g': *pos = 0x67u; break;
        case 'h': *pos = 0x68u; break;
        case 'i': *pos = 0x69u; break;
        case 'j': *pos = 0x6Au; break;
        case 'k': *pos = 0x6Bu; break;
        case 'l': *pos = 0x6Cu; break;
        case 'm': *pos = 0x6Du; break;
        case 'n': *pos = 0x6Eu; break;
        case 'o': *pos = 0x6Fu; break;
        case 'p': *pos = 0x70u; break;
        case 'q': *pos = 0x71u; break;
        case 'r': *pos = 0x72u; break;
        case 's': *pos = 0x73u; break;
        case 't': *pos = 0x74u; break;
        case 'u': *pos = 0x75u; break;
        case 'v': *pos = 0x76u; break;
        case 'w': *pos = 0x77u; break;
        case 'x': *pos = 0x78u; break;
        case 'y': *pos = 0x79u; break;
        case 'z': *pos = 0x7Au; break;
        case '{': *pos = 0x7Bu; break;
        case '|': *pos = 0x7Cu; break;
        case '}': *pos = 0x7Du; break;
        case '~': *pos = 0x7Eu; break;

        case 0: *pos = 0; return;

        default: *pos = *pc;
        }
    }
}