PgBiel · PgBiel · Jun 4, 2025 · Jun 4, 2025 · Jun 4, 2025
diff --git a/README.md b/README.md
@@ -82,7 +82,7 @@ You can use `{:spec}` to customize your output. See the Rust docs linked above f
     - For strings, `?` (and thus `repr()`) has the effect of printing them with double quotes. For floats, this ensures a `.0` appears after it, even if it doesn't have decimal digits. For integers, this doesn't change anything. Finally, for labels, the `<label>` (with `?`) is printed as `<label>` instead of `label`.
     - **TIP:** Prefer to always use `?` when you're inserting something that isn't a string, number or label, in order to ensure consistent results even if the library eventually changes the non-`?` representation.
 - After the `:`, add e.g. `_<8` to align the string to the left, padding it with as many `_`s as necessary for it to be at least `8` characters long (for example). Replace `<` by `>` for right alignment, or `^` for center alignment. (If the `_` is omitted, it defaults to ' ' (aligns with spaces).)
-    - If you prefer to specify the minimum width (the `8` there) as a separate argument to `strfmt` instead, you can specify `argument$` in place of the width, which will extract it from the integer at `argument`. For example, `_^3$` will center align the output with `_`s, where the minimum width desired is specified by the fourth positional argument (index `3`), as an integer. This means that a call such as `strfmt("{:_^3$}", 1, 2, 3, 4)` would produce `"__1__"`, as `3$` would evaluate to `4` (the value at the fourth positional argument/index `3`). Similarly, `named$` would take the width from the argument with name `named`, if it is an integer (otherwise, error).
+    - If you prefer to specify the minimum width (the `8` there) as a separate argument to `strfmt` instead, you can specify `argument$` in place of the width, which will extract it from the integer at `argument`. For example, `_^3$` will center align the output with `_`s, where the minimum width desired is specified by the fourth positional argument (index `3`), as an integer. This means that a call such as `strfmt("{v:_^3$}", 1, 2, 3, 4, v: 88)` would produce `"_88_"`, as `3$` would evaluate to `4` (the value at the fourth positional argument/index `3`). Similarly, `named$` would take the width from the argument with name `named`, if it is an integer (otherwise, error).
 - **For numbers:**
     - Specify `+` after the `:` to ensure zero or positive numbers are prefixed with `+` before them (instead of having no sign). `-` is also accepted but ignored (negative numbers always specify their sign anyways).
     - Use something like `:09` to add zeroes to the left of the number until it has at least 9 digits / characters.
@@ -147,7 +147,7 @@ Some examples:
 #import "@preview/oxifmt:0.3.0": strfmt
 
 #let s = strfmt("Left5 {:-<5}, Right6 {:=>6}, Center10 {centered: ^10?}, Left3 {tleft:_<3}", "xx", 539, tleft: "okay", centered: [a])
-#assert.eq(s, "Left5 xx---, Right6 ===539, Center10     [a]    , Left3 okay")
+#assert.eq(s, "Left5 xx---, Right6 ===539, Center10    [a]    , Left3 okay")
 // note how 'okay' didn't suffer any padding at all (it already had at least the desired total width).
 ```
 

diff --git a/oxifmt.typ b/oxifmt.typ
@@ -645,8 +645,10 @@ parameter := argument '$'
       } else if align == right {
         replacement = (fill * width-diff) + replacement
       } else if align == center {
-        let width-fill = fill * (calc.ceil(float(width-diff) / 2))
-        replacement = width-fill + replacement + width-fill
+        let half-width = calc.quo(width-diff, 2)
+        let left-fill = fill * half-width // floor div
+        let right-fill = fill * (half-width + calc.rem(width-diff, 2)) // ceil div (if adding odd fill, add 1 to the right)
+        replacement = left-fill + replacement + right-fill
       }
     }
   }

diff --git a/tests/strfmt-tests.typ b/tests/strfmt-tests.typ
@@ -17,7 +17,7 @@
   // assert.eq(strfmt("a{b}}b}", ..("b}b": 5)), "a5")
 
   // test 0 prefix with numbers, but also using 0 as a non-numeric affix
-  assert.eq(strfmt("{:08}|{0:0<8}|{0:0>8}|{0:0^8}", 120), "00000120|12000000|00000120|000120000")
+  assert.eq(strfmt("{:08}|{0:0<8}|{0:0>8}|{0:0^8}", 120), "00000120|12000000|00000120|00120000")
 
   // test other kinds of affixes / fills and alignments
   assert.eq(strfmt("{:a>8}, {:^20.10}, {:+05.4}, {:07}, {other:06?}", "b", 5.5, 11, -4, other: -30.0), "aaaaaaab,     5.5000000000    , +0011, -000004, -030.0")
@@ -182,15 +182,28 @@
 
   // Issue #28: pad with {} inside :
   assert.eq(strfmt("{:}>4}", "a"), "}}}a")
-  assert.eq(strfmt("{:}^4}", "a"), "}}a}}")
+  assert.eq(strfmt("{:}^4}", "a"), "}a}}")
   assert.eq(strfmt("{:}<4}", "a"), "a}}}")
   assert.eq(strfmt("{:{>4}", "a"), "{{{a")
-  assert.eq(strfmt("{:{^4}", "a"), "{{a{{")
+  assert.eq(strfmt("{:{^4}", "a"), "{a{{")
   assert.eq(strfmt("{:{<4}", "a"), "a{{{")
   assert.eq(strfmt("{:{^}", "a"), "a")
   assert.eq(strfmt("{:}^}", "a"), "a")
   assert.eq(strfmt("{:}}}", "a"), "a}")
 }
+// Issue #29: center alignment
+#{
+  assert.eq(strfmt("{:}^1}", "a"), "a")
+  assert.eq(strfmt("{:}^2}", "a"), "a}")
+  assert.eq(strfmt("{:}^3}", "a"), "}a}")
+  assert.eq(strfmt("{:}^4}", "a"), "}a}}")
+  assert.eq(strfmt("{:}^5}", "a"), "}}a}}")
+
+  assert.eq(strfmt("{:}>4}", "a"), "}}}a")
+  assert.eq(strfmt("{:}<4}", "a"), "a}}}")
+  assert.eq(strfmt("{:}>5}", "a"), "}}}}a")
+  assert.eq(strfmt("{:}<5}", "a"), "a}}}}")
+}
 // DOC TESTS
 #{
   // --- Quick examples ---
@@ -262,7 +275,7 @@
   }
   {
     let s = strfmt("Left5 {:_<5}, Right6 {:*>6}, Center10 {centered: ^10?}, Left3 {tleft:_<3}", "xx", 539, tleft: "okay", centered: [a])
-    assert.eq(s, "Left5 xx___, Right6 ***539, Center10     [a]    , Left3 okay")
+    assert.eq(s, "Left5 xx___, Right6 ***539, Center10    [a]    , Left3 okay")
   }
   {
     let s = strfmt("Left-padded7 numbers: {:07} {:07} {:07} {3:07}", 123, -344, 44224059, 45.32)