libs/libc: support explicit bases up to 36

[Zepp-Hanzj]

Summary

The integer conversion interfaces document explicit bases from 2 through 36. The shared lib_checkbase() helper currently rejects bases above 26 even though lib_isbasedigit() already supports digits 0-9 and letters a-z/A-Z.

Raise the explicit-base limit from 26 to 36 so strtol(), strtoul(), strtoll(), strtoull(), strtoimax(), and strtoumax() accept the full documented range. Bases below 2 and above 36 remain invalid.

Impact

Explicit bases 27 through 36 no longer fail with EINVAL. Existing base-0 detection, bases 2 through 26, and invalid-base handling are unchanged.

Testing

Automated regression coverage

apache/nuttx-apps#3688 adds dedicated ostest coverage for bases 2 through
36, all six strto* interfaces, end pointers, errno, and invalid bases 1
and 37. The test asserts at base 27 without this fix and passes with it.

NuttX sim

Built the current upstream sim:nsh configuration and ran a dedicated 117-assertion test program covering:

• every explicit base from 2 through 36
• lowercase and uppercase alphabetic digits
• all six integer conversion interfaces
• whitespace, signs, and end pointers
• base-36 64-bit limits and overflow saturation
• invalid bases 1, 37, and -2
• base-0 decimal, octal, and hexadecimal detection
• out-of-base digits, no-conversion input, and unsigned negation

BASE36-TEST BEGIN
BASE36-TEST SUMMARY total=117 passed=117 failed=0
BASE36-TEST PASS

STM32F407ZG hardware A/B

Built and flashed the same 110-assertion test program before and after this one-line change. J-Link verified both images after programming. The serial results below are from the physical STM32F407ZG target at 115200 baud.

Before fix: 69 passed, 41 failed

BASE36-TEST BEGIN
FAIL api=strtoul case=max-lower input='q#' base=27 value=0 expected=26 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='Q#' base=27 value=0 expected=26 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=27 value=0 expected=27 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='r#' base=28 value=0 expected=27 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='R#' base=28 value=0 expected=27 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=28 value=0 expected=28 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='s#' base=29 value=0 expected=28 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='S#' base=29 value=0 expected=28 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=29 value=0 expected=29 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='t#' base=30 value=0 expected=29 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='T#' base=30 value=0 expected=29 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=30 value=0 expected=30 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='u#' base=31 value=0 expected=30 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='U#' base=31 value=0 expected=30 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=31 value=0 expected=31 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='v#' base=32 value=0 expected=31 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='V#' base=32 value=0 expected=31 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=32 value=0 expected=32 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='w#' base=33 value=0 expected=32 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='W#' base=33 value=0 expected=32 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=33 value=0 expected=33 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='x#' base=34 value=0 expected=33 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='X#' base=34 value=0 expected=33 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=34 value=0 expected=34 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='y#' base=35 value=0 expected=34 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='Y#' base=35 value=0 expected=34 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=35 value=0 expected=35 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=max-lower input='z#' base=36 value=0 expected=35 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=max-upper input='Z#' base=36 value=0 expected=35 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoul case=positional-10 input='10!' base=36 value=0 expected=36 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoul case=whitespace-plus input='   +z!' base=36 value=0 expected=35 end=0 expected_end=4 errno=22 expected_errno=0
FAIL api=strtoll case=negative input='-z!' base=36 value=0 expected=18446744073709551581 end=0 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoull case=ull-simple input='Z!' base=36 value=0 expected=35 end=0 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoimax case=imax-simple input='-z!' base=36 value=0 expected=18446744073709551581 end=1 expected_end=2 errno=22 expected_errno=0
FAIL api=strtoumax case=umax-simple input='z!' base=36 value=0 expected=35 end=-134373988 expected_end=1 errno=22 expected_errno=0
FAIL api=strtoull case=ull-max input='3w5e11264sgsf!' base=36 value=0 expected=18446744073709551615 end=0 expected_end=13 errno=22 expected_errno=0
FAIL api=strtoull case=ull-overflow input='3w5e11264sgsg!' base=36 value=0 expected=18446744073709551615 end=0 expected_end=13 errno=22 expected_errno=34
FAIL api=strtoll case=ll-max input='1y2p0ij32e8e7!' base=36 value=0 expected=9223372036854775807 end=0 expected_end=13 errno=22 expected_errno=0
FAIL api=strtoll case=ll-positive-overflow input='1y2p0ij32e8e8!' base=36 value=0 expected=9223372036854775807 end=0 expected_end=13 errno=22 expected_errno=34
FAIL api=strtoll case=ll-min input='-1y2p0ij32e8e8!' base=36 value=0 expected=9223372036854775808 end=0 expected_end=14 errno=22 expected_errno=0
FAIL api=strtoll case=ll-negative-overflow input='-1y2p0ij32e8e9!' base=36 value=0 expected=9223372036854775808 end=0 expected_end=14 errno=22 expected_errno=34
BASE36-TEST SUMMARY total=110 passed=69 failed=41
BASE36-TEST FAIL

After fix: 110 passed, 0 failed

BASE36-TEST BEGIN
BASE36-TEST SUMMARY total=110 passed=110 failed=0
BASE36-TEST PASS

Style

$ tools/checkpatch.sh -f libs/libc/stdlib/lib_checkbase.c
✔️ All checks pass.

[github-actions]

MemBrowse Memory Report

hifive1-revb

• flash: .text +4 B (+0.0%, 83,356 B / 4,194,304 B, total: 2% used)
  No memory changes detected for:
• arduino-mega2560
• esp32-devkitc
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb

[acassis]

@Zepp-Hanzj suggestion: add some test to it on ostest

[Zepp-Hanzj]

Thanks for the suggestion. I added dedicated ostest regression coverage in apache/nuttx-apps#3688. It checks every explicit base from 2 through 36, lower- and upper-case digits, all six strto* interfaces, end pointers, errno, and invalid bases 1 and 37. I verified that it asserts at the first base-27 case without this fix and passes the libc test section with this fix.