rust-lang · bors · Dec 8, 2025 · Nov 29, 2025
diff --git a/library/core/src/num/int_log10.rs b/library/core/src/num/int_log10.rs
@@ -1,9 +1,11 @@
 //! These functions compute the integer logarithm of their type, assuming
 //! that someone has already checked that the value is strictly positive.
 
+use crate::num::NonZero;
+
 // 0 < val <= u8::MAX
 #[inline]
-pub(super) const fn u8(val: u8) -> u32 {
+const fn u8_impl(val: u8) -> u32 {
     let val = val as u32;
 
     // For better performance, avoid branches by assembling the solution
@@ -45,13 +47,13 @@ const fn less_than_5(val: u32) -> u32 {
 
 // 0 < val <= u16::MAX
 #[inline]
-pub(super) const fn u16(val: u16) -> u32 {
+const fn u16_impl(val: u16) -> u32 {
     less_than_5(val as u32)
 }
 
 // 0 < val <= u32::MAX
 #[inline]
-pub(super) const fn u32(mut val: u32) -> u32 {
+const fn u32_impl(mut val: u32) -> u32 {
     let mut log = 0;
     if val >= 100_000 {
         val /= 100_000;
@@ -62,7 +64,7 @@ pub(super) const fn u32(mut val: u32) -> u32 {
 
 // 0 < val <= u64::MAX
 #[inline]
-pub(super) const fn u64(mut val: u64) -> u32 {
+const fn u64_impl(mut val: u64) -> u32 {
     let mut log = 0;
     if val >= 10_000_000_000 {
         val /= 10_000_000_000;
@@ -77,66 +79,87 @@ pub(super) const fn u64(mut val: u64) -> u32 {
 
 // 0 < val <= u128::MAX
 #[inline]
-pub(super) const fn u128(mut val: u128) -> u32 {
+const fn u128_impl(mut val: u128) -> u32 {
     let mut log = 0;
     if val >= 100_000_000_000_000_000_000_000_000_000_000 {
         val /= 100_000_000_000_000_000_000_000_000_000_000;
         log += 32;
-        return log + u32(val as u32);
+        return log + u32_impl(val as u32);
     }
     if val >= 10_000_000_000_000_000 {
         val /= 10_000_000_000_000_000;
         log += 16;
     }
-    log + u64(val as u64)
+    log + u64_impl(val as u64)
 }
 
-#[cfg(target_pointer_width = "16")]
-#[inline]
-pub(super) const fn usize(val: usize) -> u32 {
-    u16(val as _)
-}
+macro_rules! define_unsigned_ilog10 {
+    ($($ty:ident => $impl_fn:ident,)*) => {$(
+        #[inline]
+        pub(super) const fn $ty(val: NonZero<$ty>) -> u32 {
+            let result = $impl_fn(val.get());
 
-#[cfg(target_pointer_width = "32")]
-#[inline]
-pub(super) const fn usize(val: usize) -> u32 {
-    u32(val as _)
-}
+            // SAFETY: Integer logarithm is monotonic non-decreasing, so the computed `result` cannot
+            // exceed the value produced for the maximum input.
+            unsafe { crate::hint::assert_unchecked(result <= const { $impl_fn($ty::MAX) }) };
 
-#[cfg(target_pointer_width = "64")]
-#[inline]
-pub(super) const fn usize(val: usize) -> u32 {
-    u64(val as _)
+            result
+        }
+    )*};
 }
 
-// 0 < val <= i8::MAX
-#[inline]
-pub(super) const fn i8(val: i8) -> u32 {
-    u8(val as u8)
+define_unsigned_ilog10! {
+    u8 => u8_impl,
+    u16 => u16_impl,
+    u32 => u32_impl,
+    u64 => u64_impl,
+    u128 => u128_impl,
 }
 
-// 0 < val <= i16::MAX
 #[inline]
-pub(super) const fn i16(val: i16) -> u32 {
-    u16(val as u16)
-}
+pub(super) const fn usize(val: NonZero<usize>) -> u32 {
+    #[cfg(target_pointer_width = "16")]
+    let impl_fn = u16;
 
-// 0 < val <= i32::MAX
-#[inline]
-pub(super) const fn i32(val: i32) -> u32 {
-    u32(val as u32)
+    #[cfg(target_pointer_width = "32")]
+    let impl_fn = u32;
+
+    #[cfg(target_pointer_width = "64")]
+    let impl_fn = u64;
+
+    // SAFETY: We have selected the correct `impl_fn`, so the converting `val` to the argument is
+    // safe.
+    impl_fn(unsafe { NonZero::new_unchecked(val.get() as _) })
 }
 
-// 0 < val <= i64::MAX
-#[inline]
-pub(super) const fn i64(val: i64) -> u32 {
-    u64(val as u64)
+macro_rules! define_signed_ilog10 {
+    ($($ty:ident => $impl_fn:ident,)*) => {$(
+        // 0 < val <= $ty::MAX
+        #[inline]
+        pub(super) const fn $ty(val: $ty) -> Option<u32> {
+            if val > 0 {
+                let result = $impl_fn(val.cast_unsigned());
+
+                // SAFETY: Integer logarithm is monotonic non-decreasing, so the computed `result`
+                // cannot exceed the value produced for the maximum input.
+                unsafe {
+                    crate::hint::assert_unchecked(result <= const { $impl_fn($ty::MAX.cast_unsigned()) });
+                }
+
+                Some(result)
+            } else {
+                None
+            }
+        }
+    )*};
 }
 
-// 0 < val <= i128::MAX
-#[inline]
-pub(super) const fn i128(val: i128) -> u32 {
-    u128(val as u128)
+define_signed_ilog10! {
+    i8 => u8_impl,
+    i16 => u16_impl,
+    i32 => u32_impl,
+    i64 => u64_impl,
+    i128 => u128_impl,
 }
 
 /// Instantiate this panic logic once, rather than for all the ilog methods

diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
@@ -3527,11 +3527,7 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_ilog10(self) -> Option<u32> {
-            if self > 0 {
-                Some(int_log10::$ActualT(self as $ActualT))
-            } else {
-                None
-            }
+            int_log10::$ActualT(self as $ActualT)
         }
 
         /// Computes the absolute value of `self`.

diff --git a/library/core/src/num/nonzero.rs b/library/core/src/num/nonzero.rs
@@ -1657,7 +1657,7 @@ macro_rules! nonzero_integer_signedness_dependent_methods {
                       without modifying the original"]
         #[inline]
         pub const fn ilog10(self) -> u32 {
-            super::int_log10::$Int(self.get())
+            super::int_log10::$Int(self)
         }
 
         /// Calculates the midpoint (average) between `self` and `rhs`.

diff --git a/tests/codegen-llvm/lib-optimizations/ilog10-range.rs b/tests/codegen-llvm/lib-optimizations/ilog10-range.rs
@@ -0,0 +1,213 @@
+//! Make sure the compiler knows the result range of `ilog10`.
+
+//@ compile-flags: -O -Z merge-functions=disabled
+
+#![crate_type = "lib"]
+
+use std::num::NonZero;
+
+// Signed integers.
+
+#[no_mangle]
+fn i8_ilog10_range(value: i8) {
+    const MAX_RESULT: u32 = i8::MAX.ilog10();
+
+    // CHECK-LABEL: @i8_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value <= 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn i16_ilog10_range(value: i16) {
+    const MAX_RESULT: u32 = i16::MAX.ilog10();
+
+    // CHECK-LABEL: @i16_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value <= 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn i32_ilog10_range(value: i32) {
+    const MAX_RESULT: u32 = i32::MAX.ilog10();
+
+    // CHECK-LABEL: @i32_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value <= 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn i64_ilog10_range(value: i64) {
+    const MAX_RESULT: u32 = i64::MAX.ilog10();
+
+    // CHECK-LABEL: @i64_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value <= 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn i128_ilog10_range(value: i128) {
+    const MAX_RESULT: u32 = i128::MAX.ilog10();
+
+    // CHECK-LABEL: @i128_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value <= 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn isize_ilog10_range(value: isize) {
+    const MAX_RESULT: u32 = isize::MAX.ilog10();
+
+    // CHECK-LABEL: @isize_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value <= 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+// Unsigned integer types.
+
+#[no_mangle]
+fn u8_ilog10_range(value: u8) {
+    const MAX_RESULT: u32 = u8::MAX.ilog10();
+
+    // CHECK-LABEL: @u8_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value == 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn u16_ilog10_range(value: u16) {
+    const MAX_RESULT: u32 = u16::MAX.ilog10();
+
+    // CHECK-LABEL: @u16_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value == 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn u32_ilog10_range(value: u32) {
+    const MAX_RESULT: u32 = u32::MAX.ilog10();
+
+    // CHECK-LABEL: @u32_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value == 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn u64_ilog10_range(value: u64) {
+    const MAX_RESULT: u32 = u64::MAX.ilog10();
+
+    // CHECK-LABEL: @u64_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value == 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn u128_ilog10_range(value: u128) {
+    const MAX_RESULT: u32 = u128::MAX.ilog10();
+
+    // CHECK-LABEL: @u128_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value == 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+#[no_mangle]
+fn usize_ilog10_range(value: usize) {
+    const MAX_RESULT: u32 = usize::MAX.ilog10();
+
+    // CHECK-LABEL: @usize_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value == 0 || value.ilog10() <= MAX_RESULT);
+    assert!(value.checked_ilog10().is_none_or(|result| result <= MAX_RESULT));
+}
+
+// Signed non-zero integers do not have `ilog10` methods.
+
+// Unsigned non-zero integers.
+
+#[no_mangle]
+fn non_zero_u8_ilog10_range(value: NonZero<u8>) {
+    // CHECK-LABEL: @non_zero_u8_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value.ilog10() <= const { u8::MAX.ilog10() });
+}
+
+#[no_mangle]
+fn non_zero_u16_ilog10_range(value: NonZero<u16>) {
+    // CHECK-LABEL: @non_zero_u16_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value.ilog10() <= const { u16::MAX.ilog10() });
+}
+
+#[no_mangle]
+fn non_zero_u32_ilog10_range(value: NonZero<u32>) {
+    // CHECK-LABEL: @non_zero_u32_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value.ilog10() <= const { u32::MAX.ilog10() });
+}
+
+#[no_mangle]
+fn non_zero_u64_ilog10_range(value: NonZero<u64>) {
+    // CHECK-LABEL: @non_zero_u64_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value.ilog10() <= const { u64::MAX.ilog10() });
+}
+
+#[no_mangle]
+fn non_zero_u128_ilog10_range(value: NonZero<u128>) {
+    // CHECK-LABEL: @non_zero_u128_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value.ilog10() <= const { u128::MAX.ilog10() });
+}
+
+#[no_mangle]
+fn non_zero_usize_ilog10_range(value: NonZero<usize>) {
+    // CHECK-LABEL: @non_zero_usize_ilog10_range(
+    // CHECK-NOT: panic
+    // CHECK: ret void
+    // CHECK-NEXT: }
+    assert!(value.ilog10() <= const { usize::MAX.ilog10() });
+}