Create and use definitions for the log2 of UTF-8 function flags #23736
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The GOT defines are now the principal ones, and the ALLOW ones are changed to be in terms of the GOT. This seems right to me, as the GOT ones are the ones anyone might actually care about. (The ALLOW ones are for weird cases.) More importantly this makes the next commit make more sense.
This commit creates new #defines for the bit positions for the flags that get passed to various functions that deal with UTF-8 input, and then redefines the flag bits as the positions shifted to the proper place. There should be no change in the code generated by this.
The previous commit #defined the bit position of various flag bits. This commit changes to use those as cases in a switch(), rather than the shifted values. This results in better generated code as the cases now reduce to: case 0: case 1: case 2: ... as opposed to previously: case 1<<0: case 1<<1: case 1<<2: ... clang and gcc were unable to see the pattern previously but now are.
tonycoz
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Sep 22, 2025
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It's an optimisation and it seems sane, but how often is that code hit?
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It should not be hit much; it does save a bit of memory, and I think I want those bit positions for other reasons. |
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Various functions that traffic in UTF-8 take a flags parameter. This series of commits creates, then uses, definitions for the log2 of those flag bits. So there is now a definition for what goes in bit position 5, and its flag is defined as
1 << 5. Compilers are better able to see the pattern in 0, 1, 2, ... than in 1<<0, 1<<1, 1<<2. These definitions will also be useful in later pull requests.