[libc-commits] [libc] [libc] Fix Off By One Errors In Printf Long Double (PR #66957)
via libc-commits
libc-commits at lists.llvm.org
Wed Sep 20 15:12:55 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libc
<details>
<summary>Changes</summary>
Two major off-by-one errors are fixed in this patch. The first is in
float_to_string.h with length_for_num, which wasn't accounting for the
implicit leading bit when calculating the length of a number, causing
a missing digit on 80 bit float max. The other off-by-one is the
ryu_long_double_constants.h (a.k.a the Mega Table) not having any
entries for the last POW10_OFFSET in POW10_SPLIT. This was also found on
80 bit float max. Finally, the integer calculation mode was using a
slightly too short integer, again on 80 bit float max, not accounting
for the mantissa width. All of these are fixed in this patch.
---
Patch is 66.76 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/66957.diff
4 Files Affected:
- (modified) libc/src/__support/float_to_string.h (+5-3)
- (modified) libc/src/__support/ryu_long_double_constants.h (+552)
- (modified) libc/test/src/stdio/sprintf_test.cpp (+79)
- (modified) libc/utils/mathtools/ryu_tablegen.py (+2-2)
``````````diff
diff --git a/libc/src/__support/float_to_string.h b/libc/src/__support/float_to_string.h
index 4714068eadf0e52..4c58651dc6884b7 100644
--- a/libc/src/__support/float_to_string.h
+++ b/libc/src/__support/float_to_string.h
@@ -157,7 +157,7 @@ LIBC_INLINE constexpr uint32_t ceil_log10_pow2(const uint32_t e) {
LIBC_INLINE constexpr uint32_t length_for_num(const uint32_t idx,
const uint32_t mantissa_width) {
//+8 to round up when dividing by 9
- return (ceil_log10_pow2(idx) + ceil_log10_pow2(mantissa_width) +
+ return (ceil_log10_pow2(idx) + ceil_log10_pow2(mantissa_width + 1) +
(BLOCK_SIZE - 1)) /
BLOCK_SIZE;
// return (ceil_log10_pow2(16 * idx + mantissa_width) + 8) / 9;
@@ -666,7 +666,7 @@ FloatToString<long double>::get_positive_block(int block_index) {
// ----------------------------- INT CALC MODE -----------------------------
const int32_t SHIFT_CONST = CALC_SHIFT_CONST;
const uint64_t MAX_POW_2_SIZE =
- exponent + CALC_SHIFT_CONST - (BLOCK_SIZE * block_index);
+ pos_exp + CALC_SHIFT_CONST - (BLOCK_SIZE * block_index);
const uint64_t MAX_POW_5_SIZE =
internal::log2_pow5(BLOCK_SIZE * block_index);
const uint64_t MAX_INT_SIZE =
@@ -680,8 +680,10 @@ FloatToString<long double>::get_positive_block(int block_index) {
val = internal::get_table_positive<4096>(pos_exp, block_index);
} else if (MAX_INT_SIZE < 8192) {
val = internal::get_table_positive<8192>(pos_exp, block_index);
- } else {
+ } else if (MAX_INT_SIZE < 16384) {
val = internal::get_table_positive<16384>(pos_exp, block_index);
+ } else {
+ val = internal::get_table_positive<16384 + 128>(pos_exp, block_index);
}
#endif
const uint32_t shift_amount = SHIFT_CONST + pos_exp - exponent;
diff --git a/libc/src/__support/ryu_long_double_constants.h b/libc/src/__support/ryu_long_double_constants.h
index 8415423e9eddd6a..86640bcc8257007 100644
--- a/libc/src/__support/ryu_long_double_constants.h
+++ b/libc/src/__support/ryu_long_double_constants.h
@@ -35403,6 +35403,558 @@ constexpr uint64_t POW10_SPLIT[][5] = {
{8185529170695989288u, 251935u, 0u, 0u, 0u},
{4647388653739187u, 0u, 0u, 0u, 0u},
{4647389u, 0u, 0u, 0u, 0u},
+ {1u, 0u, 0u, 0u, 1666406u},
+ {9167511163728910775u, 3312060066959522888u, 1295184565790726114u, 14514316166628409175u, 467615u},
+ {18446650963712978694u, 11459123952047835623u, 11203169122561999106u, 12474589757305876786u, 2263011u},
+ {1727375103581005166u, 6279996614298463960u, 7709863957368393064u, 16687049419988932499u, 1149488u},
+ {5260295235157421525u, 18426378431810315116u, 1049713953025921878u, 12343052908124526721u, 3504815u},
+ {3705581585852188490u, 3335423218796647794u, 5009356519446298754u, 17358475006776455890u, 3071434u},
+ {14296650234967904607u, 13533728612605645886u, 13550853390885990417u, 17206365355322613797u, 2749915u},
+ {18409334644427041092u, 1794178469698007910u, 17611594257294438978u, 1708051658308162884u, 3019512u},
+ {4754135742177139480u, 6231107125027989758u, 17105560207999383557u, 17277465141864323237u, 2595660u},
+ {18358242171314739190u, 5662514190210093154u, 11287743438560124974u, 5452201045844425276u, 2058811u},
+ {17761256625928321051u, 17212837789613283598u, 9527998849657635872u, 11639251005171736777u, 1601676u},
+ {5821492835406745926u, 2889087753330502654u, 17816699099621606956u, 1830985569848452224u, 878190u},
+ {12963632653576508465u, 16198926776608324708u, 18116681369755801167u, 3835252232019257168u, 913381u},
+ {9574571567457348478u, 3277569375660351599u, 18148476178141229221u, 8447587411821609647u, 210151u},
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+ {2894580858817241479u, 16914896149213534922u, 14780479720941674...
[truncated]
``````````
</details>
https://github.com/llvm/llvm-project/pull/66957
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