The following code, simple as it is, fails to work. I suspect it's a brain short on my part, and willingly accept the public humiliation. Perhaps it's an actual problem that I am just now uncovering. I am new to the toolset, so all bets are off. The tool is a bit on the dated side. Perhaps there is an update that I'm missing.
TIA for any help.
John
IDE-Version: µVision V4.72.10.0 Copyright (C) 2013 ARM Ltd and ARM Germany GmbH. All rights reserved.
Tool Version Numbers: Toolchain: MDK-ARM Standard Cortex-M only Version: 4.72.1.0 Toolchain Path: C:\Keil\ARM\ARMCC\bin\ C Compiler: Armcc.Exe V5.03.0.76 Assembler: Armasm.Exe V5.03.0.76 Linker/Locator: ArmLink.Exe V5.03.0.76 Librarian: ArmAr.Exe V5.03.0.76 Hex Converter: FromElf.Exe V5.03.0.76 CPU DLL: SARMCM3.DLL V4.72.1.0 Dialog DLL: DARMP1.DLL V1.22.0.11 Target DLL: UL2CM3.DLL V1.150.11.0 Dialog DLL: TARMP1.DLL V1.22.0.11
float gain; float fTemp; uint32_t lTemp; uint16_t temp; // On entry, gain is 27.893 fTemp = gain * 1000.0; // gain - preserve three decimal places // fTemp now 27893.0 lTemp = (uint32_t)fTemp; // lTemp now 0x6C5F (27743, while I expect 27893) temp = lTemp & 0xFFFF; // temp now 27743 // WTH?
floats is about the only means of computing 2 * = 3.94
float is NOT precise
I changed the floats to doubles. waaay too many code float just because there is a decimal point somewhere.
I think float is enough for your case, double is unnecessary. But I am not so sure. The below code runs on Windows:
#include <stdio.h> #include <stdint.h> int main(void) { float gain = 27.893; float fTemp; uint32_t lTemp; uint16_t temp; fTemp = gain * 1000.0; lTemp = (uint32_t)fTemp; temp = lTemp & 0xFFFF; printf("%f, %d, %d", fTemp, lTemp, temp); }
And the result is:
27893.000000, 27893, 27893 Process returned 26 (0x1A) execution time : -0.000 s Press any key to continue.
Thanks, all. I used the double when float was clearly broken, and that fixed the problem. That it works on Windows is irrelevant, insofar as I am not targeting a Windows platform. But I agree - it should work.
Seems to work fine on 4.71a, 4.73 and 4.74. both with and without FPU on a Cortex-M4. Don't have 4.72 installed.
I'd recommend including math.h and using the f suffix for float constants, but either way John's code functions.
// On entry, gain is 27.893 fTemp = gain * 1000.0; // gain - preserve three decimal places // fTemp now 27893.0 lTemp = (uint32_t)fTemp; // lTemp now 0x6C5F (27743, while I expect 27893)
27893=0x6CF5 27743=0x6C5F F and 5 are swapped. Maybe the magic is at (uint32_t)?