Stop signed left shift overflows in ed25519
The new ed25519 code contains some signed left shifts of negative numbers, which clang identifies as runtime errors.
Under -ftrapv, this causes a trap/crash.
Without -ftrapv, this causes about 100 warnings during the tests like: crypto/ed25519_simple: src/ext/ed25519/ref10/ge_scalarmult_base.c:42:48: runtime error: left shift of negative value -2 (log attached)
A patch is attached that performs potentially overflowing left shifts in unsigned arithmetic. Macros SHL64 and SHL32 are defined for convenience.
This is my first patch using git format-patch with a changes entry - let me know if it needs revising.
Version: tor 2.6.?-alpha git: 5190ec0bc4c22d7bab756e21db6e357ba07379c4
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