3 files changed, 132 insertions, 0 deletions
diff --git a/pnm/private/bitwise.scm b/pnm/private/bitwise.scm
new file mode 100644
index 0000000..a2f2f74
--- /dev/null
+++ b/pnm/private/bitwise.scm
@@ -0,0 +1,38 @@
+;;; R7RS-PNM --- Library for reading and writing PNM (Portable Any Map) files for R7RS
+;;; Copyright © 2024 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; This file is part of R7RS-PNM.
+;;;
+;;; R7RS-PNM is free software: you can redistribute it and/or modify it
+;;; under the terms of the GNU Lesser General Public License as published
+;;; by the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; R7RS-PNM is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;;; GNU Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public License
+;;; along with R7RS-PNM. If not, see <https://www.gnu.org/licenses/>.
+
+(define-library (pnm private bitwise)
+  (export bitwise-and
+          bitwise-ior
+          arithmetic-shift
+          bit-set?
+          copy-bit)
+  (import (scheme base))
+  (cond-expand
+    ((library (scheme bitwise))
+     (import (only (scheme bitwise)
+                   bitwise-and bitwise-ior arithmetic-shift
+                   bit-set? copy-bit)))
+    ((library (srfi 60))
+     (import (only (srfi 60)
+                   bitwise-and bitwise-ior arithmetic-shift
+                   bit-set? copy-bit)))
+    ((library (srfi 151))
+     (import (only (srfi 151)
+                   bitwise-and bitwise-ior arithmetic-shift
+                   bit-set? copy-bit)))))
diff --git a/pnm/private/checker.scm b/pnm/private/checker.scm
new file mode 100644
index 0000000..e212948
--- /dev/null
+++ b/pnm/private/checker.scm
@@ -0,0 +1,65 @@
+;;; R7RS-PNM --- Library for reading and writing PNM (Portable Any Map) files for R7RS
+;;; Copyright © 2024 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; This file is part of R7RS-PNM.
+;;;
+;;; R7RS-PNM is free software: you can redistribute it and/or modify it
+;;; under the terms of the GNU Lesser General Public License as published
+;;; by the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; R7RS-PNM is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;;; GNU Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public License
+;;; along with R7RS-PNM. If not, see <https://www.gnu.org/licenses/>.
+
+(define-library (pnm private checker)
+  (export make-xy-checker
+          make-value-checker
+          make-boolean-value-checker)
+  (import (scheme base)
+          (scheme case-lambda)
+          (pnm image))
+  (begin
+    (define (make-xy-checker width height)
+      (lambda (x y)
+        (when (or (not (exact-integer? x))
+                  (< x 0)
+                  (<= width x))
+          (error (string-append  "`x` must be an integer such that 0 <= `x` < "
+                                 (number->string width))
+                 x))
+        (when (and (not (exact-integer? y))
+                   (< y 0)
+                   (<= height y))
+          (error (string-append  "`y` must be an integer such that 0 <= `y` < "
+                                 (number->string width))
+                 y))))
+
+    (define (make-value-checker maxval sym)
+      (define message
+        (string-append "`" (symbol->string sym) "`"
+                       " must be an integer such that 0 < "
+                       "`" (symbol->string sym) "`"
+                       " < "
+                       (number->string maxval)))
+      (lambda (v)
+        (when (or (not (exact-integer? v))
+                  (< v 0)
+                  (< maxval v))
+          (error message v))))
+
+    (define (make-boolean-value-checker)
+      (lambda (v)
+        (when (not (boolean? v))
+          (error "`v` must be a boolean value" v))))
+
+    (define (split-value v)
+      (values (modulo (quotient v 256) 256)
+              (modulo v 256)))
+
+    (define (combine-values l r)
+      (+ (* 256 l) r))))
diff --git a/pnm/private/double-byte.scm b/pnm/private/double-byte.scm
new file mode 100644
index 0000000..fd40336
--- /dev/null
+++ b/pnm/private/double-byte.scm
@@ -0,0 +1,29 @@
+;;; R7RS-PNM --- Library for reading and writing PNM (Portable Any Map) files for R7RS
+;;; Copyright © 2024 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; This file is part of R7RS-PNM.
+;;;
+;;; R7RS-PNM is free software: you can redistribute it and/or modify it
+;;; under the terms of the GNU Lesser General Public License as published
+;;; by the Free Software Foundation, either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; R7RS-PNM is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;;; GNU Lesser General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Lesser General Public License
+;;; along with R7RS-PNM. If not, see <https://www.gnu.org/licenses/>.
+
+(define-library (pnm private double-byte)
+  (export split-double-byte combine-bytes)
+  (import (scheme base)
+          (pnm private bitwise))
+  (begin
+    (define (split-double-byte v)
+      (values (arithmetic-shift v -8)
+              (bitwise-and v 255)))
+
+    (define (combine-bytes l r)
+      (bitwise-ior (arithmetic-shift l 8) r))))