os: add support for %f to pnprintf

This is the lazy man's %f support. Print the decimal part of the number,
then append a decimal point, then print the first two digits of the
fractional part. So %f in sigsafe printing is really %.2f.

No boundary checks in place here.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Keith Packard <keithp@keithp.com>

2 files changed, 42 insertions, 1 deletions

diff --git a/os/log.c b/os/log.c
index 213906420..7b5c9ee1c 100644
--- a/os/log.c
+++ b/os/log.c
@@ -351,7 +351,16 @@ pnprintf(char *string, size_t size, const char *f, va_list args)
             for (i = 0; i < p_len && s_idx < size - 1; i++)
                 string[s_idx++] = number[i];
             break;
-
+        case 'f':
+            {
+                double d = va_arg(args, double);
+                FormatDouble(d, number);
+                p_len = strlen_sigsafe(number);
+
+                for (i = 0; i < p_len && s_idx < size - 1; i++)
+                    string[s_idx++] = number[i];
+            }
+            break;
         default:
             va_arg(args, char*);
             string[s_idx++] = '%';
diff --git a/os/utils.c b/os/utils.c
index e396ba4b5..3ba6499c4 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -1990,6 +1990,38 @@ FormatUInt64(uint64_t num, char *string)
     string[len] = '\0';
 }
 
+/**
+ * Format a double number as %.2f.
+ */
+void
+FormatDouble(double dbl, char *string)
+{
+    int slen = 0;
+    uint64_t frac;
+
+    frac = (dbl > 0 ? dbl : -dbl) * 100.0;
+    frac %= 100;
+
+    /* write decimal part to string */
+    if (dbl < 0 && dbl > -1)
+        string[slen++] = '-';
+    FormatInt64((int64_t)dbl, &string[slen]);
+
+    while(string[slen] != '\0')
+        slen++;
+
+    /* append fractional part, but only if we have enough characters. We
+     * expect string to be 21 chars (incl trailing \0) */
+    if (slen <= 17) {
+        string[slen++] = '.';
+        if (frac < 10)
+            string[slen++] = '0';
+
+        FormatUInt64(frac, &string[slen]);
+    }
+}
+
+
 /* Format a number into a hexadecimal string in a signal safe manner. The string
  * should be at least 17 characters in order to handle all uint64_t values. */
 void