/**
 * Part of the D programming language runtime library.
 */

/*
 *  Copyright (C) 2004-2006 by Digital Mars, www.digitalmars.com
 *  Written by Walter Bright
 *
 *  This software is provided 'as-is', without any express or implied
 *  warranty. In no event will the authors be held liable for any damages
 *  arising from the use of this software.
 *
 *  Permission is granted to anyone to use this software for any purpose,
 *  including commercial applications, and to alter it and redistribute it
 *  freely, in both source and binary form, subject to the following
 *  restrictions:
 *
 *  o  The origin of this software must not be misrepresented; you must not
 *     claim that you wrote the original software. If you use this software
 *     in a product, an acknowledgment in the product documentation would be
 *     appreciated but is not required.
 *  o  Altered source versions must be plainly marked as such, and must not
 *     be misrepresented as being the original software.
 *  o  This notice may not be removed or altered from any source
 *     distribution.
 */

/*
 *  Modified by Sean Kelly <sean@f4.ca> for use with Tango.
 */

/* This code handles decoding UTF strings for foreach_reverse loops.
 * There are 6 combinations of conversions between char, wchar,
 * and dchar, and 2 of each of those.
 */

private import util.utf;

/**********************************************/
/* 1 argument versions */

// dg is D, but _aApplyRcd() is C
extern (D) typedef int delegate(void *) dg_t;

extern (C) int _aApplyRcd1(in char[] aa, dg_t dg)
{   int result;

    debug(apply) printf("_aApplyRcd1(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;

        i--;
        d = aa[i];
        if (d & 0x80)
        {   char c = cast(char)d;
            uint j;
            uint m = 0x3F;
            d = 0;
            while ((c & 0xC0) != 0xC0)
            {   if (i == 0)
                    onUnicodeError("Invalid UTF-8 sequence", 0);
                i--;
                d |= (c & 0x3F) << j;
                j += 6;
                m >>= 1;
                c = aa[i];
            }
            d |= (c & m) << j;
        }
        result = dg(cast(void *)&d);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRcd1.unittest\n");

    char[] s = "hello"c;
    int i;

    foreach_reverse(dchar d; s)
    {
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(dchar d; s)
    {
        //printf("i = %d, d = %x\n", i, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); break;
            case 1:     assert(d == '\U00100456'); break;
            case 2:     assert(d == '\u1234'); break;
            case 3:     assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 4);
}

/*****************************/

extern (C) int _aApplyRwd1(in wchar[] aa, dg_t dg)
{   int result;

    debug(apply) printf("_aApplyRwd1(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;

        i--;
        d = aa[i];
        if (d >= 0xDC00 && d <= 0xDFFF)
        {   if (i == 0)
                onUnicodeError("Invalid UTF-16 sequence", 0);
            i--;
            d = ((aa[i] - 0xD7C0) << 10) + (d - 0xDC00);
        }
        result = dg(cast(void *)&d);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRwd1.unittest\n");

    wchar[] s = "hello"w;
    int i;

    foreach_reverse(dchar d; s)
    {
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(dchar d; s)
    {
        //printf("i = %d, d = %x\n", i, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); break;
            case 1:     assert(d == '\U00100456'); break;
            case 2:     assert(d == '\u1234'); break;
            case 3:     assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 4);
}

/*****************************/

extern (C) int _aApplyRcw1(in char[] aa, dg_t dg)
{   int result;

    debug(apply) printf("_aApplyRcw1(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;
        wchar w;

        i--;
        w = aa[i];
        if (w & 0x80)
        {   char c = cast(char)w;
            uint j;
            uint m = 0x3F;
            d = 0;
            while ((c & 0xC0) != 0xC0)
            {   if (i == 0)
                    onUnicodeError("Invalid UTF-8 sequence", 0);
                i--;
                d |= (c & 0x3F) << j;
                j += 6;
                m >>= 1;
                c = aa[i];
            }
            d |= (c & m) << j;

            if (d <= 0xFFFF)
                w = cast(wchar) d;
            else
            {
                w = cast(wchar) ((((d - 0x10000) >> 10) & 0x3FF) + 0xD800);
                result = dg(cast(void *)&w);
                if (result)
                    break;
                w = cast(wchar) (((d - 0x10000) & 0x3FF) + 0xDC00);
            }
        }
        result = dg(cast(void *)&w);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRcw1.unittest\n");

    char[] s = "hello"c;
    int i;

    foreach_reverse(wchar d; s)
    {
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(wchar d; s)
    {
        //printf("i = %d, d = %x\n", i, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); break;
            case 1:     assert(d == 0xDBC1); break;
            case 2:     assert(d == 0xDC56); break;
            case 3:     assert(d == 0x1234); break;
            case 4:     assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);
}

/*****************************/

extern (C) int _aApplyRwc1(in wchar[] aa, dg_t dg)
{   int result;

    debug(apply) printf("_aApplyRwc1(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;
        char c;

        i--;
        d = aa[i];
        if (d >= 0xDC00 && d <= 0xDFFF)
        {   if (i == 0)
                onUnicodeError("Invalid UTF-16 sequence", 0);
            i--;
            d = ((aa[i] - 0xD7C0) << 10) + (d - 0xDC00);
        }

        if (d & ~0x7F)
        {
            char[4] buf;

            auto b = toUTF8(buf, d);
            foreach (char c2; b)
            {
                result = dg(cast(void *)&c2);
                if (result)
                    return result;
            }
            continue;
        }
        c = cast(char)d;
        result = dg(cast(void *)&c);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRwc1.unittest\n");

    wchar[] s = "hello"w;
    int i;

    foreach_reverse(char d; s)
    {
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(char d; s)
    {
        //printf("i = %d, d = %x\n", i, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); break;
            case 1:     assert(d == 0xF4); break;
            case 2:     assert(d == 0x80); break;
            case 3:     assert(d == 0x91); break;
            case 4:     assert(d == 0x96); break;
            case 5:     assert(d == 0xE1); break;
            case 6:     assert(d == 0x88); break;
            case 7:     assert(d == 0xB4); break;
            case 8:     assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 9);
}

/*****************************/

extern (C) int _aApplyRdc1(in dchar[] aa, dg_t dg)
{   int result;

    debug(apply) printf("_aApplyRdc1(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0;)
    {   dchar d = aa[--i];
        char c;

        if (d & ~0x7F)
        {
            char[4] buf;

            auto b = toUTF8(buf, d);
            foreach (char c2; b)
            {
                result = dg(cast(void *)&c2);
                if (result)
                    return result;
            }
            continue;
        }
        else
        {
            c = cast(char)d;
        }
        result = dg(cast(void *)&c);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRdc1.unittest\n");

    dchar[] s = "hello"d;
    int i;

    foreach_reverse(char d; s)
    {
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(char d; s)
    {
        //printf("i = %d, d = %x\n", i, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); break;
            case 1:     assert(d == 0xF4); break;
            case 2:     assert(d == 0x80); break;
            case 3:     assert(d == 0x91); break;
            case 4:     assert(d == 0x96); break;
            case 5:     assert(d == 0xE1); break;
            case 6:     assert(d == 0x88); break;
            case 7:     assert(d == 0xB4); break;
            case 8:     assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 9);
}

/*****************************/

extern (C) int _aApplyRdw1(in dchar[] aa, dg_t dg)
{   int result;

    debug(apply) printf("_aApplyRdw1(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d = aa[--i];
        wchar w;

        if (d <= 0xFFFF)
            w = cast(wchar) d;
        else
        {
            w = cast(wchar) ((((d - 0x10000) >> 10) & 0x3FF) + 0xD800);
            result = dg(cast(void *)&w);
            if (result)
                break;
            w = cast(wchar) (((d - 0x10000) & 0x3FF) + 0xDC00);
        }
        result = dg(cast(void *)&w);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRdw1.unittest\n");

    dchar[] s = "hello"d;
    int i;

    foreach_reverse(wchar d; s)
    {
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(wchar d; s)
    {
        //printf("i = %d, d = %x\n", i, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); break;
            case 1:     assert(d == 0xDBC1); break;
            case 2:     assert(d == 0xDC56); break;
            case 3:     assert(d == 0x1234); break;
            case 4:     assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);
}


/****************************************************************************/
/* 2 argument versions */

// dg is D, but _aApplyRcd2() is C
extern (D) typedef int delegate(void *, void *) dg2_t;

extern (C) int _aApplyRcd2(in char[] aa, dg2_t dg)
{   int result;
    size_t i;
    size_t len = aa.length;

    debug(apply) printf("_aApplyRcd2(), len = %d\n", len);
    for (i = len; i != 0; )
    {   dchar d;

        i--;
        d = aa[i];
        if (d & 0x80)
        {   char c = cast(char)d;
            uint j;
            uint m = 0x3F;
            d = 0;
            while ((c & 0xC0) != 0xC0)
            {   if (i == 0)
                    onUnicodeError("Invalid UTF-8 sequence", 0);
                i--;
                d |= (c & 0x3F) << j;
                j += 6;
                m >>= 1;
                c = aa[i];
            }
            d |= (c & m) << j;
        }
        result = dg(&i, cast(void *)&d);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRcd2.unittest\n");

    char[] s = "hello"c;
    int i;

    foreach_reverse(k, dchar d; s)
    {
        assert(k == 4 - i);
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(k, dchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        switch (i)
        {
            case 0:     assert(d == 'b'); assert(k == 8); break;
            case 1:     assert(d == '\U00100456'); assert(k == 4); break;
            case 2:     assert(d == '\u1234'); assert(k == 1); break;
            case 3:     assert(d == 'a'); assert(k == 0); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 4);
}

/*****************************/

extern (C) int _aApplyRwd2(in wchar[] aa, dg2_t dg)
{   int result;

    debug(apply) printf("_aApplyRwd2(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;

        i--;
        d = aa[i];
        if (d >= 0xDC00 && d <= 0xDFFF)
        {   if (i == 0)
                onUnicodeError("Invalid UTF-16 sequence", 0);
            i--;
            d = ((aa[i] - 0xD7C0) << 10) + (d - 0xDC00);
        }
        result = dg(&i, cast(void *)&d);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRwd2.unittest\n");

    wchar[] s = "hello"w;
    int i;

    foreach_reverse(k, dchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        assert(k == 4 - i);
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(k, dchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        switch (i)
        {
            case 0:     assert(k == 4); assert(d == 'b'); break;
            case 1:     assert(k == 2); assert(d == '\U00100456'); break;
            case 2:     assert(k == 1); assert(d == '\u1234'); break;
            case 3:     assert(k == 0); assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 4);
}

/*****************************/

extern (C) int _aApplyRcw2(in char[] aa, dg2_t dg)
{   int result;

    debug(apply) printf("_aApplyRcw2(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;
        wchar w;

        i--;
        w = aa[i];
        if (w & 0x80)
        {   char c = cast(char)w;
            uint j;
            uint m = 0x3F;
            d = 0;
            while ((c & 0xC0) != 0xC0)
            {   if (i == 0)
                    onUnicodeError("Invalid UTF-8 sequence", 0);
                i--;
                d |= (c & 0x3F) << j;
                j += 6;
                m >>= 1;
                c = aa[i];
            }
            d |= (c & m) << j;

            if (d <= 0xFFFF)
                w = cast(wchar) d;
            else
            {
                w = cast(wchar) ((((d - 0x10000) >> 10) & 0x3FF) + 0xD800);
                result = dg(&i, cast(void *)&w);
                if (result)
                    break;
                w = cast(wchar) (((d - 0x10000) & 0x3FF) + 0xDC00);
            }
        }
        result = dg(&i, cast(void *)&w);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRcw2.unittest\n");

    char[] s = "hello"c;
    int i;

    foreach_reverse(k, wchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        assert(k == 4 - i);
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(k, wchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        switch (i)
        {
            case 0:     assert(k == 8); assert(d == 'b'); break;
            case 1:     assert(k == 4); assert(d == 0xDBC1); break;
            case 2:     assert(k == 4); assert(d == 0xDC56); break;
            case 3:     assert(k == 1); assert(d == 0x1234); break;
            case 4:     assert(k == 0); assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);
}

/*****************************/

extern (C) int _aApplyRwc2(in wchar[] aa, dg2_t dg)
{   int result;

    debug(apply) printf("_aApplyRwc2(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d;
        char c;

        i--;
        d = aa[i];
        if (d >= 0xDC00 && d <= 0xDFFF)
        {   if (i == 0)
                onUnicodeError("Invalid UTF-16 sequence", 0);
            i--;
            d = ((aa[i] - 0xD7C0) << 10) + (d - 0xDC00);
        }

        if (d & ~0x7F)
        {
            char[4] buf;

            auto b = toUTF8(buf, d);
            foreach (char c2; b)
            {
                result = dg(&i, cast(void *)&c2);
                if (result)
                    return result;
            }
            continue;
        }
        c = cast(char)d;
        result = dg(&i, cast(void *)&c);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRwc2.unittest\n");

    wchar[] s = "hello"w;
    int i;

    foreach_reverse(k, char d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        assert(k == 4 - i);
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(k, char d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        switch (i)
        {
            case 0:     assert(k == 4); assert(d == 'b'); break;
            case 1:     assert(k == 2); assert(d == 0xF4); break;
            case 2:     assert(k == 2); assert(d == 0x80); break;
            case 3:     assert(k == 2); assert(d == 0x91); break;
            case 4:     assert(k == 2); assert(d == 0x96); break;
            case 5:     assert(k == 1); assert(d == 0xE1); break;
            case 6:     assert(k == 1); assert(d == 0x88); break;
            case 7:     assert(k == 1); assert(d == 0xB4); break;
            case 8:     assert(k == 0); assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 9);
}

/*****************************/

extern (C) int _aApplyRdc2(in dchar[] aa, dg2_t dg)
{   int result;

    debug(apply) printf("_aApplyRdc2(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d = aa[--i];
        char c;

        if (d & ~0x7F)
        {
            char[4] buf;

            auto b = toUTF8(buf, d);
            foreach (char c2; b)
            {
                result = dg(&i, cast(void *)&c2);
                if (result)
                    return result;
            }
            continue;
        }
        else
        {   c = cast(char)d;
        }
        result = dg(&i, cast(void *)&c);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRdc2.unittest\n");

    dchar[] s = "hello"d;
    int i;

    foreach_reverse(k, char d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        assert(k == 4 - i);
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(k, char d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        switch (i)
        {
            case 0:     assert(k == 3); assert(d == 'b'); break;
            case 1:     assert(k == 2); assert(d == 0xF4); break;
            case 2:     assert(k == 2); assert(d == 0x80); break;
            case 3:     assert(k == 2); assert(d == 0x91); break;
            case 4:     assert(k == 2); assert(d == 0x96); break;
            case 5:     assert(k == 1); assert(d == 0xE1); break;
            case 6:     assert(k == 1); assert(d == 0x88); break;
            case 7:     assert(k == 1); assert(d == 0xB4); break;
            case 8:     assert(k == 0); assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 9);
}

/*****************************/

extern (C) int _aApplyRdw2(in dchar[] aa, dg2_t dg)
{   int result;

    debug(apply) printf("_aApplyRdw2(), len = %d\n", aa.length);
    for (size_t i = aa.length; i != 0; )
    {   dchar d = aa[--i];
        wchar w;

        if (d <= 0xFFFF)
            w = cast(wchar) d;
        else
        {
            w = cast(wchar) ((((d - 0x10000) >> 10) & 0x3FF) + 0xD800);
            result = dg(&i, cast(void *)&w);
            if (result)
                break;
            w = cast(wchar) (((d - 0x10000) & 0x3FF) + 0xDC00);
        }
        result = dg(&i, cast(void *)&w);
        if (result)
            break;
    }
    return result;
}

unittest
{
    debug(apply) printf("_aApplyRdw2.unittest\n");

    dchar[] s = "hello"d;
    int i;

    foreach_reverse(k, wchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        assert(k == 4 - i);
        switch (i)
        {
            case 0:     assert(d == 'o'); break;
            case 1:     assert(d == 'l'); break;
            case 2:     assert(d == 'l'); break;
            case 3:     assert(d == 'e'); break;
            case 4:     assert(d == 'h'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);

    s = "a\u1234\U00100456b";
    i = 0;
    foreach_reverse(k, wchar d; s)
    {
        //printf("i = %d, k = %d, d = %x\n", i, k, d);
        switch (i)
        {
            case 0:     assert(k == 3); assert(d == 'b'); break;
            case 1:     assert(k == 2); assert(d == 0xDBC1); break;
            case 2:     assert(k == 2); assert(d == 0xDC56); break;
            case 3:     assert(k == 1); assert(d == 0x1234); break;
            case 4:     assert(k == 0); assert(d == 'a'); break;
            default:    assert(0);
        }
        i++;
    }
    assert(i == 5);
}