Speed up empty String creation slightly #6573
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As @DirkMuller found out in esp8266#6568, there is a difference in code executed between `String str(nullptr)` and `String str("")`, but in the end the actual object is identical. It's a few bytes of code, but every little bit counts. Update the default `String()` constructor to use `nullptr` and not `""`. This will remove a constant literal load and the execution of the String::copy method and strlen().
devyte
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Sep 30, 2019
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earlephilhower
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This reverts commit 1aeea12.
earlephilhower
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PR esp8266#6573 introduced a corner case where a blind String() without any initialization was in an in invalid state because the buffer and len would not be updated properly. Concatenating to the empty string could cause a failure. Now, set the default state in ::init() to SSO (which is what happened before when we were using String(char *s="")) and fix the crash.
earlephilhower
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PR esp8266#6573 introduced a corner case where a blind String() without any initialization was in an in invalid state because the buffer and len would not be updated properly. Concatenating to the empty string could cause a failure. Now, set the default state in ::init() to SSO (which is what happened before when we were using String(char *s="")) and fix the crash.
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* Replace ASM block w/C marco for PSTR GAS doesn't support the C language idiom of catenating two strings together with quotes (i.e. "x" "y" === "xy"). Specify the section attribute fully in the section attribute, instead, to allow this. * Fix WString optimization PR #6573 introduced a corner case where a blind String() without any initialization was in an in invalid state because the buffer and len would not be updated properly. Concatenating to the empty string could cause a failure. Now, set the default state in ::init() to SSO (which is what happened before when we were using String(char *s="")) and fix the crash.
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As @dirkmueller (sorry bout typo!) found out in #6568, there is a difference in code
executed between
String str(nullptr)andString str(""), but in theend the actual object is identical. It's a few bytes of code, but every
little bit counts.
Update the default
String()constructor to usenullptrand not"".This will remove a constant literal load and the execution of the
String::copy method and strlen().