[libc-commits] [libc] [libc] Fix incorrect unsigned comparison (PR #135595)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Wu Yingcong (yingcong-wu)

<details>
<summary>Changes</summary>

There is a problem with such unsigned comparison pattern:
```
if(unsigned_a - unsigned_b > 0) { /* only NOT go here when unsigned_a==unsigned_b */ }
```
When `unsigned_a` < `unsigned_b`, the result will still be `>0` due to underflow.
This patch fixes two of the occurrences I found.

---
Full diff: https://github.com/llvm/llvm-project/pull/135595.diff


1 Files Affected:

- (modified) libc/src/stdio/printf_core/float_dec_converter.h (+2-2) 


``````````diff
diff --git a/libc/src/stdio/printf_core/float_dec_converter.h b/libc/src/stdio/printf_core/float_dec_converter.h
index ee5549825a6f2..178f228527f68 100644
--- a/libc/src/stdio/printf_core/float_dec_converter.h
+++ b/libc/src/stdio/printf_core/float_dec_converter.h
@@ -192,7 +192,7 @@ template <WriteMode write_mode> class FloatWriter {
         RET_IF_RESULT_NEGATIVE(writer->write({block_buffer, digits_to_write}));
       }
       RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
-      if (buffered_digits - digits_to_write > 0) {
+      if (buffered_digits > digits_to_write) {
         // Write the digits after the decimal point.
         RET_IF_RESULT_NEGATIVE(
             writer->write({block_buffer + digits_to_write,
@@ -222,7 +222,7 @@ template <WriteMode write_mode> class FloatWriter {
         RET_IF_RESULT_NEGATIVE(writer->write(MAX_BLOCK_DIGIT, digits_to_write));
       }
       RET_IF_RESULT_NEGATIVE(writer->write(DECIMAL_POINT));
-      if ((BLOCK_SIZE * max_block_count) - digits_to_write > 0) {
+      if ((BLOCK_SIZE * max_block_count) > digits_to_write) {
         RET_IF_RESULT_NEGATIVE(writer->write(
             MAX_BLOCK_DIGIT, (BLOCK_SIZE * max_block_count) - digits_to_write));
       }

``````````

</details>


https://github.com/llvm/llvm-project/pull/135595