On Mon, Oct 14, 2013 at 06:23:33PM +0200, Andrew Jones wrote:
> arm can't do arbitrary divisions without software support. Usually
> libgcc would jump in here, but depending on the toolchain used that may
> or may not work. Luckily, we only care about two types of divisions.
> Divide by 10 and divide by 16. Divide by 16 is already covered by gcc
> since it's a power of two. Divide by 10 can be hacked up using a
> multiplication and shift.
Isn't this just a matter of supplying a few libc implementations to
handle div_by_0 and that sort? I'm pretty sure we had that working in
the kvm-selftest for ARM thingy that allowed you to use the standard '/'
operator in C code.... I suspect there will be more users of this
eventually.
Or wait, do you mean 'long long' operations by arbitrary? In that case,
I'm less sure... A library implementation to support the operator would
still be preferred IMHO.
>
> Signed-off-by: Andrew Jones <drjones@xxxxxxxxxx>
> ---
> lib/divmod.h | 20 ++++++++++++++++++++
> lib/printf.c | 27 ++++++++++++++-------------
> 2 files changed, 34 insertions(+), 13 deletions(-)
> create mode 100644 lib/divmod.h
>
> diff --git a/lib/divmod.h b/lib/divmod.h
> new file mode 100644
> index 0000000000000..c0f04d7d8386d
> --- /dev/null
> +++ b/lib/divmod.h
> @@ -0,0 +1,20 @@
> +#ifndef _DIVMOD_H_
> +#define _DIVMOD_H_
> +#ifdef __arm__
> +static inline long long div10(long long n)
> +{
> + /*
> + * multiply n by 2^32/10 and the result of n/10
> + * will be in the upper word
> + */
> + return (n * 0x1999999aU) >> 32;
> +}
> +static inline int mod10(long long n)
> +{
> + return n - div10(n) * 10;
> +}
> +#else
> +#define div10(n) ((n) / 10)
> +#define mod10(n) ((n) % 10)
> +#endif
> +#endif
> diff --git a/lib/printf.c b/lib/printf.c
> index 867eb1926f742..9fb8133868c7a 100644
> --- a/lib/printf.c
> +++ b/lib/printf.c
> @@ -1,4 +1,5 @@
> #include "libcflat.h"
> +#include "divmod.h"
>
> typedef struct pstream {
> char *buffer;
> @@ -23,7 +24,7 @@ void print_str(pstream_t *p, const char *s)
>
> static char digits[16] = "0123456789abcdef";
>
> -void print_int(pstream_t *ps, long long n, int base)
> +void print_int(pstream_t *ps, long long n)
> {
> char buf[sizeof(long) * 3 + 2], *p = buf;
> int s = 0, i;
> @@ -34,8 +35,8 @@ void print_int(pstream_t *ps, long long n, int base)
> }
>
> while (n) {
> - *p++ = digits[n % base];
> - n /= base;
> + *p++ = digits[mod10(n)];
> + n = div10(n);
> }
>
> if (s)
> @@ -57,14 +58,14 @@ void print_int(pstream_t *ps, long long n, int base)
> print_str(ps, buf);
> }
>
> -void print_unsigned(pstream_t *ps, unsigned long long n, int base)
> +void print_unsigned(pstream_t *ps, unsigned long long n)
> {
> char buf[sizeof(long) * 3 + 1], *p = buf;
> int i;
>
> while (n) {
> - *p++ = digits[n % base];
> - n /= base;
> + *p++ = digits[n % 16];
> + n /= 16;
> }
>
> if (p == buf)
> @@ -116,32 +117,32 @@ int vsnprintf(char *buf, int size, const char *fmt, va_list va)
> case 'd':
> switch (nlong) {
> case 0:
> - print_int(&s, va_arg(va, int), 10);
> + print_int(&s, va_arg(va, int));
> break;
> case 1:
> - print_int(&s, va_arg(va, long), 10);
> + print_int(&s, va_arg(va, long));
> break;
> default:
> - print_int(&s, va_arg(va, long long), 10);
> + print_int(&s, va_arg(va, long long));
> break;
> }
> break;
> case 'x':
> switch (nlong) {
> case 0:
> - print_unsigned(&s, va_arg(va, unsigned), 16);
> + print_unsigned(&s, va_arg(va, unsigned));
> break;
> case 1:
> - print_unsigned(&s, va_arg(va, unsigned long), 16);
> + print_unsigned(&s, va_arg(va, unsigned long));
> break;
> default:
> - print_unsigned(&s, va_arg(va, unsigned long long), 16);
> + print_unsigned(&s, va_arg(va, unsigned long long));
> break;
> }
> break;
> case 'p':
> print_str(&s, "0x");
> - print_unsigned(&s, (unsigned long)va_arg(va, void *), 16);
> + print_unsigned(&s, (unsigned long)va_arg(va, void *));
> break;
> case 's':
> print_str(&s, va_arg(va, const char *));
> --
> 1.8.1.4
>
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