[GH-ISSUE #1608] implicit conversion from 'float' to 'double' [-Wdouble-promotion] #1370

New issue

Closed

opened 2026-02-28 01:29:48 +03:00 by kerem · 3 comments

kerem commented

2026-02-28 01:29:48 +03:00

Owner

Originally created by @fixus971 on GitHub (May 16, 2023).
Original GitHub issue: https://github.com/tzapu/WiFiManager/issues/1608

Hardware
WiFimanager Branch/Release: Master
Esp32

Problem description:
warning: implicit conversion from 'float' to 'double' to match other operand of binary expression [-Wdouble-promotion]

Line 2269:
p.replace(FPSTR(T_2),(String)((temperatureRead()+32)*1.8));

*1.8 Issue at end of line

Solution
replace with *1.8f

Originally created by @fixus971 on GitHub (May 16, 2023). Original GitHub issue: https://github.com/tzapu/WiFiManager/issues/1608 Hardware WiFimanager Branch/Release: Master Esp32 Problem description: warning: implicit conversion from 'float' to 'double' to match other operand of binary expression [-Wdouble-promotion] Line 2269: p.replace(FPSTR(T_2),(String)((temperatureRead()+32)*1.8)); *1.8 Issue at end of line Solution replace with *1.8f

kerem

2026-02-28 01:29:48 +03:00

closed this issue
added the
bug
label

kerem commented

2026-02-28 01:29:48 +03:00

Author

Owner

@fixus971 commented on GitHub (May 17, 2023):

Hi. Is warning of compiler in c17 version.

even if normally this warning is not signaled.. it is still a problem for
32 bit CPUs.

I corrected many similar arithmetic calculations because I saw the
explanation and I tested it: the 32bit CPUs of the Arduino world suffer a
lot from double counts that go beyond 32bit. Needed .. but just put an "f"
and everything falls into place

Il mer 17 mag 2023, 03:11 Shawn A @.***> ha scritto:

I don't get these warnings

build_flags: -Wall -Wdouble-promotion

what flags?

—
Reply to this email directly, view it on GitHub
https://github.com/tzapu/WiFiManager/issues/1608#issuecomment-1550547688,
or unsubscribe
https://github.com/notifications/unsubscribe-auth/ACRX5MW7TLCUPQQHL2KKK7DXGQQT5ANCNFSM6AAAAAAYEHQD6I
.
You are receiving this because you authored the thread.Message ID:
@.***>

@fixus971 commented on GitHub (May 17, 2023): Hi. Is warning of compiler in c17 version. even if normally this warning is not signaled.. it is still a problem for 32 bit CPUs. I corrected many similar arithmetic calculations because I saw the explanation and I tested it: the 32bit CPUs of the Arduino world suffer a lot from double counts that go beyond 32bit. Needed .. but just put an "f" and everything falls into place Il mer 17 mag 2023, 03:11 Shawn A ***@***.***> ha scritto: > I don't get these warnings > > build_flags: -Wall -Wdouble-promotion > > what flags? > > — > Reply to this email directly, view it on GitHub > <https://github.com/tzapu/WiFiManager/issues/1608#issuecomment-1550547688>, > or unsubscribe > <https://github.com/notifications/unsubscribe-auth/ACRX5MW7TLCUPQQHL2KKK7DXGQQT5ANCNFSM6AAAAAAYEHQD6I> > . > You are receiving this because you authored the thread.Message ID: > ***@***.***> >

kerem commented

2026-02-28 01:29:48 +03:00

Author

Owner

@fixus971 commented on GitHub (May 17, 2023):

Some info about double calc on arduino hardware:
https://forum.arduino.cc/t/8bit-vs-32bit-floating-point-calculations/543123/11

I see that int and a float is 4 bytes and a double is 8 bytes.
after that i read and tested that double require more software time. (Double)

I used platformio with:

[env:Esp32]
framework = arduino
platform = espressif32
board = az-delivery-devkit-v4
upload_speed = 921600

monitor_speed = 115200
monitor_filters = direct ;EscChar to console wo filtering = colors

build_unflags =
-std=c++11
-std=gnu++11
-Os

build_flags =
-DCORE_DEBUG_LEVEL=ARDUHAL_LOG_LEVEL_DEBUG ;=4
-O3
-std=c++17
-std=gnu++17
-Wall ;en warnings questionable constructions that are easy to avoid
-Wextra ;en extra warning flags that are not enabled by -Wall.
-Wdouble-promotion ; warn double soft64b:.9(def=double)->.9f
-Wimplicit-fallthrough ; warn if switch case without break
-Wreturn-type -Werror=return-type ; no return(x) -> CPU Exception hard to found

@fixus971 commented on GitHub (May 17, 2023): Some info about double calc on arduino hardware: https://forum.arduino.cc/t/8bit-vs-32bit-floating-point-calculations/543123/11 I see that int and a float is 4 bytes and a double is 8 bytes. after that i read and tested that double require more software time. (Double) I used platformio with: [env:Esp32] framework = arduino platform = espressif32 board = az-delivery-devkit-v4 upload_speed = 921600 monitor_speed = 115200 monitor_filters = direct ;EscChar to console wo filtering = colors build_unflags = -std=c++11 -std=gnu++11 -Os build_flags = -DCORE_DEBUG_LEVEL=ARDUHAL_LOG_LEVEL_DEBUG ;=4 -O3 -std=c++17 -std=gnu++17 -Wall ;en warnings questionable constructions that are easy to avoid -Wextra ;en extra warning flags that are not enabled by -Wall. -Wdouble-promotion ; warn double soft64b:.9(def=double)->.9f -Wimplicit-fallthrough ; warn if switch case without break -Wreturn-type -Werror=return-type ; no return(x) -> CPU Exception hard to found

kerem commented

2026-02-28 01:29:48 +03:00

Author

Owner

@tablatronix commented on GitHub (May 17, 2023):

Thanks for that!

@tablatronix commented on GitHub (May 17, 2023): Thanks for that!