1 files changed, 36 insertions, 10 deletions
diff --git a/internal/psalter/psalter.go b/internal/psalter/psalter.go
index 815f660..3e50c53 100644
--- a/internal/psalter/psalter.go
+++ b/internal/psalter/psalter.go
@@ -25,22 +25,48 @@ func DrbVerse(hebrewPsalm, lectionaryVerse int) int {
 }
 
 // HebrewToVulgateChapter maps a Masoretic psalm number to its Vulgate chapter.
+// For the split psalms (116, 147) it returns the chapter of the FIRST verse;
+// use HebrewToVulgate for the verse-accurate mapping.
 func HebrewToVulgateChapter(h int) int {
+	c, _ := HebrewToVulgate(h, 1)
+	return c
+}
+
+// HebrewToVulgate maps a Masoretic (modern) psalm number and verse to the
+// Vulgate chapter and verse. Most psalms differ only by a one-off chapter shift
+// with the verse unchanged, but four spans are joined or split, so the verse
+// carries an offset there:
+//
+//	Hebrew 9  = Vulgate 9:1-21     Hebrew 10 = Vulgate 9:22-39   (10:v -> 9:v+21)
+//	Hebrew 114 = Vulgate 113:1-8   Hebrew 115 = Vulgate 113:9-26 (115:v -> 113:v+8)
+//	Hebrew 116:1-9  = Vulgate 114  Hebrew 116:10-19 = Vulgate 115:1-10 (116:v>=10 -> 115:v-9)
+//	Hebrew 147:1-11 = Vulgate 146  Hebrew 147:12-20 = Vulgate 147:1-9  (147:v>=12 -> 147:v-11)
+func HebrewToVulgate(h, v int) (chapter, verse int) {
 	switch {
 	case h <= 8 || h >= 148:
-		return h
-	case h >= 9 && h <= 10:
-		return 9
+		return h, v
+	case h == 9:
+		return 9, v
+	case h == 10:
+		return 9, v + 21
 	case h >= 11 && h <= 113:
-		return h - 1
-	case h >= 114 && h <= 115:
-		return 113
+		return h - 1, v
+	case h == 114:
+		return 113, v
+	case h == 115:
+		return 113, v + 8
 	case h == 116:
-		return 114
+		if v <= 9 {
+			return 114, v
+		}
+		return 115, v - 9
 	case h >= 117 && h <= 146:
-		return h - 1
+		return h - 1, v
 	case h == 147:
-		return 146
+		if v <= 11 {
+			return 146, v
+		}
+		return 147, v - 11
 	}
-	return h
+	return h, v
 }