Wrong formatting of doubles?

[Michal Terepeta <michalt@google.com>]

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Hi,

We're working on a RISC-V system and using musl as our libc. A recent change
in musl seems to have caused wrong formatting (printf) of double values:
https://git.musl-libc.org/cgit/musl/commit/src/stdio/vfprintf.c?id=572a2e2eb91f00f2f25d301cfb50f435e7ae16b3

Using a simple binary to print max double [1] with the current code I get:

```
The maximum value of a double (printf %e): 1.348676e+308
The maximum value of a double (printf %E): 1.348676E+308
The maximum value of a double (printf %g): 3.13486e+308
```

With the patch [2] that reverts most of the above change, I get the expected
output:

```
The maximum value of a double (printf %e): 1.797693e+308
The maximum value of a double (printf %E): 1.797693E+308
The maximum value of a double (printf %g): 1.79769e+308
```

It'd be great if someone could take a look if they can also repro and perhaps
revert the change?

Many thanks!

Michal



[1] Repro program:

```
#include <float.h>
#include <stdio.h>

int main() {
  printf("The maximum value of a double (printf %%e): %e\n", DBL_MAX);
  printf("The maximum value of a double (printf %%E): %E\n", DBL_MAX);
  printf("The maximum value of a double (printf %%g): %g\n", DBL_MAX);
  return 0;
}

```


[2] Patch to test:

```
diff --git a/src/stdio/vfprintf.c b/src/stdio/vfprintf.c
index 010041ca6c..01004158bf 100644
--- a/src/stdio/vfprintf.c
+++ b/src/stdio/vfprintf.c
@@ -180,12 +180,8 @@

 static int fmt_fp(FILE *f, long double y, int w, int p, int fl, int t, int ps)
 {
-       int bufsize = (ps==BIGLPRE)
-               ? (LDBL_MANT_DIG+28)/29 + 1 +          // mantissa expansion
-                 (LDBL_MAX_EXP+LDBL_MANT_DIG+28+8)/9  // exponent expansion
-               : (DBL_MANT_DIG+28)/29 + 1 +
-                 (DBL_MAX_EXP+DBL_MANT_DIG+28+8)/9;
-       uint32_t big[bufsize];
+       uint32_t big[(LDBL_MANT_DIG+28)/29 + 1          // mantissa expansion
+               + (LDBL_MAX_EXP+LDBL_MANT_DIG+28+8)/9]; // exponent expansion
        uint32_t *a, *d, *r, *z;
        int e2=0, e, i, j, l;
        char buf[9+LDBL_MANT_DIG/4], *s;
```

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