casaroli commented on code in PR #21537:
URL: https://github.com/apache/nuttx/pull/21537#discussion_r4501772648
##########
drivers/sensors/Kconfig:
##########
@@ -29,6 +29,7 @@ config SENSORS_USE_FLOAT
config SENSORS_USE_B16
bool "Use b16_t as data type for sensors"
+ select LIBC_BFORMAT_B16
Review Comment:
With this option every `%hf` in a binary format is a `b16_t`, also for a
real `float` member. `struct sensor_eng` has `float voltage[4]`
(include/nuttx/uorb.h:1102), and apps/system/uorb/sensor/eng.c prints it with
`eng0:%hf`..`eng3:%hf`, so a B16 build now prints 3300.0 as 17742.25, and
uorb_generator stores `b16_t` bits into the float.
Fix: change `voltage` to `sensor_data_t voltage[4]` in include/nuttx/uorb.h
in this PR, as all the other sensor members.
##########
libs/libc/stream/lib_libvscanf.c:
##########
@@ -1101,7 +1111,36 @@ static int vscanf_internal(FAR struct lib_instream_s
*stream, FAR int *lastc,
/* Return the float value */
# ifdef CONFIG_HAVE_FLOAT
- *pf = fvalue;
+# ifdef CONFIG_LIBC_BFORMAT_B16
+ if (modifier == H_MOD && !varg)
+ {
+ /* Binary format: %hf is a b16_t, rounded to
+ * the nearest value and saturated.
+ */
+
+ FAR b16_t *pb16 = (FAR b16_t *)pf;
+
+ if (fvalue >= 32768.0f)
+ {
+ *pb16 = b16MAX;
+ }
+ else if (fvalue <= -32768.0f)
+ {
+ *pb16 = b16MIN;
+ }
+ else
+ {
+ float r = fvalue * 65536.0f;
Review Comment:
The product is computed in `float` (24-bit mantissa), so above 256 the
result is not the nearest `b16_t`: 300.0001 gives 19660806 (nearest is
19660807) and 32767.99 is 15 LSB off.
Fix: under `CONFIG_HAVE_DOUBLE`, convert with `strtod()` and round `dvalue *
65536.0`, or say "rounded in float" in the commit message and the PR body.
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