Add a "fork" of musl as //fusl.

fusl/src/stdlib/wcstod.c

+#include "shgetc.h"
+#include "floatscan.h"
+#include "stdio_impl.h"
+#include <wchar.h>
+#include <wctype.h>
+
+/* This read function heavily cheats. It knows:
+ *  (1) len will always be 1
+ *  (2) non-ascii characters don't matter */
+
+static size_t do_read(FILE *f, unsigned char *buf, size_t len)
+{
+        size_t i;
+        const wchar_t *wcs = f->cookie;
+
+        if (!wcs[0]) wcs=L"@";
+        for (i=0; i<f->buf_size && wcs[i]; i++)
+                f->buf[i] = wcs[i] < 128 ? wcs[i] : '@';
+        f->rpos = f->buf;
+        f->rend = f->buf + i;
+        f->cookie = (void *)(wcs+i);
+
+        if (i && len) {
+                *buf = *f->rpos++;
+                return 1;
+        }
+        return 0;
+}
+
+static long double wcstox(const wchar_t *s, wchar_t **p, int prec)
+{
+        wchar_t *t = (wchar_t *)s;
+        unsigned char buf[64];
+        FILE f = {0};
+        f.flags = 0;
+        f.rpos = f.rend = 0;
+        f.buf = buf + 4;
+        f.buf_size = sizeof buf - 4;
+        f.lock = -1;
+        f.read = do_read;
+        while (iswspace(*t)) t++;
+        f.cookie = (void *)t;
+        shlim(&f, 0);
+        long double y = __floatscan(&f, prec, 1);
+        if (p) {
+                size_t cnt = shcnt(&f);
+                *p = cnt ? t + cnt : (wchar_t *)s;
+        }
+        return y;
+}
+
+float wcstof(const wchar_t *restrict s, wchar_t **restrict p)
+{
+        return wcstox(s, p, 0);
+}
+
+double wcstod(const wchar_t *restrict s, wchar_t **restrict p)
+{
+        return wcstox(s, p, 1);
+}
+
+long double wcstold(const wchar_t *restrict s, wchar_t **restrict p)
+{
+        return wcstox(s, p, 2);
+}