From 28bbf00908f6518d5a8470b0081a298d3c22f024 Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Wed, 20 Mar 2024 18:18:53 -0600
Subject: [PATCH] FatPtr_index, FatPtr_prepend

---
 libfatptr/libfatptr.c | 25 +++++++++++++++++++++----
 libfatptr/libfatptr.h | 15 +++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/libfatptr/libfatptr.c b/libfatptr/libfatptr.c
index 92ae739..39a64b9 100644
--- a/libfatptr/libfatptr.c
+++ b/libfatptr/libfatptr.c
@@ -5,8 +5,8 @@ struct FatPtr *
 FatPtr_append(struct FatPtr *p, FatPtr_scalar_t c){
 	FatPtr_vector_t t;
 
-	if(p == NULL || (p->s + (sizeof *(p->v)) > p->a
-			&& FatPtr_grow(p, sizeof FatPtr_scalar_t) == NULL))
+	if(p == NULL || (p->s + (sizeof (FatPtr_scalar_t)) > p->a
+			&& FatPtr_grow(p, sizeof (FatPtr_scalar_t)) == NULL))
 		return NULL;
 	(p->v)[(p->s)++] = c;
 	return p;
@@ -15,7 +15,7 @@ FatPtr_append(struct FatPtr *p, FatPtr_scalar_t c){
 struct FatPtr *
 FatPtr_construct(struct FatPtr *p){
 
-	return FatPtr_grow(FatPtr_initialize(p), sizeof FatPtr_scalar_t);
+	return FatPtr_grow(FatPtr_initialize(p), sizeof (FatPtr_scalar_t));
 }
 
 struct FatPtr *
@@ -50,6 +50,23 @@ FatPtr_initialize(struct FatPtr *p){
 	return p;
 }
 
+FatPtr_vector_t
+FatPtr_index(struct FatPtr *p, size_t index){
+
+	return p == NULL
+		? NULL
+		: &p->v[index];
+}
+
+struct FatPtr *
+FatPtr_prepend(struct FatPtr *p, FatPtr_vector_t s, size_t units){
+	size_t i;
+
+	if(FatPtr_shiftleft(p, units) != NULL)
+		for(i = 0; units --> 0; p->v[i] = *s++);
+	return p;
+}
+
 struct FatPtr *
 FatPtr_shiftleft(struct FatPtr *p, size_t units){
 	size_t i;
@@ -64,7 +81,7 @@ struct FatPtr *
 FatPtr_shiftright(struct FatPtr *p, size_t units){
 	size_t i;
 
-	if(FatPtr_grow(p, units * (sizeof FatPtr_scalar_t)) == NULL)
+	if(FatPtr_grow(p, units * (sizeof (FatPtr_scalar_t))) == NULL)
 		return NULL;
 	for(i = 0; i < p->s; ++i)
 		(p->v)[i + units] = (p->v)[i];
diff --git a/libfatptr/libfatptr.h b/libfatptr/libfatptr.h
index a685cc9..cc5443f 100644
--- a/libfatptr/libfatptr.h
+++ b/libfatptr/libfatptr.h
@@ -42,12 +42,27 @@ struct FatPtr *FatPtr_destruct(struct FatPtr *p);
  * Grows p's maximum length by units (in sizeof char). */
 struct FatPtr *FatPtr_grow(struct FatPtr *p, size_t units);
 
+/* FatPtr_index
+ * - FatPtr *p: object to index
+ * - size_t index: index of the scalar to get
+ * Returns a pointer to the FatPtr_scalar_t at the given index within the
+ * vector, or NULL if p was NULL. */
+FatPtr_vector_t FatPtr_index(struct FatPtr *p, size_t index);
+
 /* FatPtr_initialize
  * - FatPtr *p: object to initialize
  * Returns p.
  * Initializes p to zero values. */
 struct FatPtr *FatPtr_initialize(struct FatPtr *p);
 
+/* FatPtr_prepend
+ * - FatPtr *p: object to which to prepend
+ * - FatPtr_vector_t s: vector to prepend
+ * - size_t units: amount of units from the vector to prepend
+ * Prepends units of s to the vector in p. Returns NULL if a memory allocation
+ * failed and p otherwise. */
+struct FatPtr *FatPtr_prepend(struct FatPtr *p, FatPtr_vector_t s, size_t units);
+
 /* FatPtr_shiftleft
  * - FatPtr *p: object to shift
  * - size_t units: units (in sizeof *v) by which to shift p