From 1e42e3f8b2a362acbf6f5b422c2b3121fb37b367 Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Thu, 31 Aug 2023 19:29:18 -0400
Subject: [PATCH] trimfront, trimend

---
 libfatptr/libfatptr.c | 57 +++++++++++++++++++++++++++----------------
 libfatptr/libfatptr.h | 56 +++++++++++++++++++++++++++++++++++-------
 2 files changed, 83 insertions(+), 30 deletions(-)

diff --git a/libfatptr/libfatptr.c b/libfatptr/libfatptr.c
index 753327f..92ae739 100644
--- a/libfatptr/libfatptr.c
+++ b/libfatptr/libfatptr.c
@@ -1,18 +1,12 @@
-#include <stdlib.h> /* free(3), malloc(3), realloc(3) */
-#include <string.h> /* strncpy(3), size_t */
+#include <stdlib.h> /* free(3), malloc(3), realloc(3), size_t */
 #include "libfatptr.h"
 
-/* quick and dirty ASCII edition */
-
-/* Size by which to grow memory allocations. */
-static size_t FatPtr_growinterval = 100; /* in sizeof chars */
-
 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, FatPtr_growinterval) == NULL))
+			&& FatPtr_grow(p, sizeof FatPtr_scalar_t) == NULL))
 		return NULL;
 	(p->v)[(p->s)++] = c;
 	return p;
@@ -21,18 +15,7 @@ FatPtr_append(struct FatPtr *p, FatPtr_scalar_t c){
 struct FatPtr *
 FatPtr_construct(struct FatPtr *p){
 
-	return FatPtr_grow(FatPtr_initialize(p), FatPtr_growinterval);
-}
-
-char *
-FatPtr_convert(struct FatPtr *p){
-	char *r;
-
-	/* allocation might be wrong */
-	return (p == NULL || (r = malloc(p->s * (sizeof *(p->v)))) == NULL)
-		? NULL
-		: strncpy(r, p->v, p->s)
-	;
+	return FatPtr_grow(FatPtr_initialize(p), sizeof FatPtr_scalar_t);
 }
 
 struct FatPtr *
@@ -68,5 +51,37 @@ FatPtr_initialize(struct FatPtr *p){
 }
 
 struct FatPtr *
-FatPtr_trimfront(struct FatPtr *p, size_t units){
+FatPtr_shiftleft(struct FatPtr *p, size_t units){
+	size_t i;
+
+	if(p != NULL)
+		for(i = 0; i < p->s; ++i)
+			(p->v)[i] = (p->v)[i + units];
+	return p;
+}
+
+struct FatPtr *
+FatPtr_shiftright(struct FatPtr *p, size_t units){
+	size_t i;
+
+	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];
+	p->s += units;
+	return p;
+}
+
+struct FatPtr *
+FatPtr_trimend(struct FatPtr *p, size_t units){
+
+	if(p != NULL)
+		p->s -= units;
+	return p;
+}
+
+struct FatPtr *
+FatPtr_trimfront(struct FatPtr *p, size_t units){
+
+	return FatPtr_trimend(FatPtr_shiftleft(p, units), units);
 }
diff --git a/libfatptr/libfatptr.h b/libfatptr/libfatptr.h
index a2fcbdd..a685cc9 100644
--- a/libfatptr/libfatptr.h
+++ b/libfatptr/libfatptr.h
@@ -18,23 +18,61 @@ struct FatPtr{
  * - FatPtr *p: object to which to append
  * - FatPtr_scalar_t c: scalar to be appended
  * Returns NULL if the operation failed (due to malloc(3)) or if p was NULL.
- * Otherwise returns p. */
+ * Otherwise returns p.
+ * Appends c to p. */
 struct FatPtr *FatPtr_append(struct FatPtr *p, FatPtr_scalar_t c);
 
+/* FatPtr_construct
+ * - FatPtr *p: object to be constructed
+ * Returns p.
+ * Initializes p and grows its maximum length to a reasonable amount of units.
+ */
 struct FatPtr *FatPtr_construct(struct FatPtr *p);
 
-/* FatPtr_convert
- * - FatPtr *p: object to convert
- * Returns NULL if the operation failed (due to malloc(3)) or if p was NULL.
- * Otherwise returns a malloc(3)d char * with the current content of p, which
- * should be free(3)d when no longer in use. */
-char *FatPtr_convert(struct FatPtr *p);
-
 /* FatPtr_destruct
  * - FatPtr *p: object to destruct
- * Returns NULL. */
+ * Returns NULL.
+ * Destroys p without leaking memory. */
 struct FatPtr *FatPtr_destruct(struct FatPtr *p);
 
+/* FatPtr_grow
+ * - FatPtr *p: object to grow
+ * - size_t units: units (in sizeof char) by which to grow p
+ * Returns p.
+ * Grows p's maximum length by units (in sizeof char). */
 struct FatPtr *FatPtr_grow(struct FatPtr *p, size_t units);
+
+/* FatPtr_initialize
+ * - FatPtr *p: object to initialize
+ * Returns p.
+ * Initializes p to zero values. */
 struct FatPtr *FatPtr_initialize(struct FatPtr *p);
+
+/* FatPtr_shiftleft
+ * - FatPtr *p: object to shift
+ * - size_t units: units (in sizeof *v) by which to shift p
+ * Returns p.
+ * Shifts members of p left by units, leaving the last units members intact. */
+struct FatPtr *FatPtr_shiftleft(struct FatPtr *p, size_t units);
+
+/* FatPtr_shiftright
+ * - FatPtr *p: object to shift
+ * - size_t units: units (in sizeof *v) by which to shift p
+ * Returns p.
+ * Shifts members of p right by units, leaving the first units members intact.
+ */
+struct FatPtr *FatPtr_shiftright(struct FatPtr *p, size_t units);
+
+/* FatPtr_trimend
+ * - FatPtr *p: object to trim
+ * - size_t units: units (in sizeof *v) by which to shift p
+ * Returns p.
+ * Removes the last units members of p from p. */
+struct FatPtr *FatPtr_trimend(struct FatPtr *p, size_t units);
+
+/* FatPtr_trimfront
+ * - FatPtr *p: object to trim
+ * - size_t units: units (in sizeof *v) by which to shift p
+ * Returns p.
+ * Removes the first units members of p from p. */
 struct FatPtr *FatPtr_trimfront(struct FatPtr *p, size_t units);