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author | Petteri Aimonen <jpa@git.mail.kapsi.fi> | 2013-01-29 22:10:37 +0200 |
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committer | Petteri Aimonen <jpa@git.mail.kapsi.fi> | 2013-01-29 22:10:37 +0200 |
commit | e4b55179d1f53c42916f5e62fb83789973bf4b01 (patch) | |
tree | 4505321c4c14bdca6362b1e1bb1054c3588a4543 /example_avr_double/README.txt | |
parent | 2392d255749715ad337d3f5e23d3de7f2065e3dd (diff) |
Add an example of handling doubles on AVR platform.
Diffstat (limited to 'example_avr_double/README.txt')
-rw-r--r-- | example_avr_double/README.txt | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/example_avr_double/README.txt b/example_avr_double/README.txt new file mode 100644 index 00000000..0090d729 --- /dev/null +++ b/example_avr_double/README.txt @@ -0,0 +1,22 @@ +Some processors/compilers, such as AVR-GCC, do not support the double +datatype. Instead, they have sizeof(double) == 4. Because protocol +binary format uses the double encoding directly, this causes trouble +if the protocol in .proto requires double fields. + +This directory contains a solution to this problem. It uses uint64_t +to store the raw wire values, because its size is correct on all +platforms. The file double_conversion.c provides functions that +convert these values to/from floats, without relying on compiler +support. + +To use this method, you need to make two modifications to your code: + +1) Change all 'double' fields into 'fixed64' in the .proto. + +2) Whenever writing to a 'double' field, use float_to_double(). + +3) Whenever reading a 'double' field, use double_to_float(). + +The conversion routines should be as accurate as the float datatype can +be. Furthermore, they should handle all special values (NaN, inf, denormalized +numbers) correctly. There are testcases in test_conversions.c. |