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Found free extra 256 bytes of RAM eliminate _clz use from libgcc 

Believe it or not, changing / 2^31 to >>31 saved 256 bytes in the "d" segment.

The reason is that GCC version prior to 4.3.5 does not have a count_leading_zeros (clz) assembler macro, so it uses a 256 byte lookup table called _clz
The _clz table gets pulled in if you do 64 bit division.
This tiny change is the only place that we do long long division.
Changing to a shift saves 256 bytes of ram.
This commit is contained in:
justinbeech 2012-02-17 09:46:05 +00:00
parent d0c67debee
commit 5255512bf9
1 changed files with 3 additions and 3 deletions
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6
libraries/AP_Baro/AP_Baro_MS5611.cpp
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@ -212,10 +212,10 @@ void AP_Baro_MS5611::_calculate()
SENS = (int64_t)C1 * 32768 + ((int64_t)C3 * dT) / 256; SENS = (int64_t)C1 * 32768 + ((int64_t)C3 * dT) / 256;
if (TEMP < 2000){ // second order temperature compensation if (TEMP < 2000){ // second order temperature compensation
int64_t T2 = (((int64_t)dT)*dT) / 2147483648UL; int64_t T2 = (((int64_t)dT)*dT) >> 31;
int64_t Aux_64 = (TEMP-2000)*(TEMP-2000); int64_t Aux_64 = (TEMP-2000)*(TEMP-2000);
int64_t OFF2 = 5*Aux_64/2; int64_t OFF2 = (5*Aux_64)>>1;
int64_t SENS2 = 5*Aux_64/4; int64_t SENS2 = (5*Aux_64)>>2;
TEMP = TEMP - T2; TEMP = TEMP - T2;
OFF = OFF - OFF2; OFF = OFF - OFF2;
SENS = SENS - SENS2; SENS = SENS - SENS2;