libc: carry the rounding out of the leading digit in %f

src/lib/libc/stdio.c

@@ -341,6 +341,20 @@ float_to_str(fmtcb_t *cb, void *aux,
   size_t total = 0;
   int significands = fp->decimals > 0 ? fp->decimals : 6;
 
+  // Round half up at the last printed digit before the layout is fixed:
+  // a carry out of the leading digit adds one (9.998 -> "10.00", not "9.00")
+  int digits = significands + e10;
+  if(digits >= 0) {
+    uint64_t r = 1ULL << 59;
+    for(int i = 0; i < digits; i++)
+      r /= 10;
+    mantissa += r;
+    if(mantissa >= (1ULL << 60)) {
+      mantissa /= 10;
+      e10++;
+    }
+  }
+
   int chars = flt_count_output_chars(sign, e10, significands, fp);
   int pad = fp->width - chars;
 
@@ -368,11 +382,6 @@ float_to_str(fmtcb_t *cb, void *aux,
     }
   }
 
-  uint64_t r = 1ULL << 59;
-  for(int i = 0; i < significands; i++)
-    r /= 10;
-  mantissa += r;
-
   for(int i = 0; i < significands; i++) {
 
     mantissa *= 10;

src/platform/stm32f4/stm32f4_ccm.c

@@ -37,5 +37,6 @@ stm32f4_ccm_init(void)
   heap_add_mem(0x10000000 + sizeof(cpu_t), CRASHLOG_ADDR,
                MEM_TYPE_LOCAL, 5);
 
+  crashlog_init((void *)CRASHLOG_ADDR);
   crashlog_recover();
 }