commit - e3b4721f113543c97e51e1b1b2f18e82dda160ff
commit + 1ce4d806ce9d151bca7396796272505d06c710e3
blob - /dev/null
blob + e922e78991e4005a5a31b4382707f077c5080639 (mode 644)
--- /dev/null
+++ 2-7-input
+0x7de65afe 15 4 0x7de6aafe
+0xadd230f1 23 6 0xad2e30f1
+0x0feb3112 31 9 0xf06b3112
+0xa0b0c118 2 2 0xa0b0c11e
+0x001992ba 17 8 0x001a6eba
+0xabcdef01 12 9 0xabcdf0f1
+0x12345678 27 7 0x1dd45678
+0x92fab3da 9 5 0x92fab03a
+0x1ba83dea 17 11 0x1babc26a
+
blob - /dev/null
blob + 9633d797704f5907de41f816ff2b2f97a444f360 (mode 644)
--- /dev/null
+++ 2-7-output
+Type input line x n p expected
+ %x %d %d %x
+result = 0x7de6aafe, expect = 0x7de6aafe
+result = 0xad2e30f1, expect = 0xad2e30f1
+result = 0xf06b3112, expect = 0xf06b3112
+result = 0xa0b0c11e, expect = 0xa0b0c11e
+result = 0x1a6eba, expect = 0x1a6eba
+result = 0xabcdf0f1, expect = 0xabcdf0f1
+result = 0x1dd45678, expect = 0x1dd45678
+result = 0x92fab03a, expect = 0x92fab03a
+result = 0x1babc26a, expect = 0x1babc26a
blob - /dev/null
blob + 96ab4ba2b480274348292e36ff1759dc0f6a29b5 (mode 644)
--- /dev/null
+++ 2-7.c
+/* 2-7 Write a function invert(x,p,n) that returns x with the n bits that begin
+ * at position p inverted (i.e., 1 changed into 0 and vice versa), leaving the
+ * others unchanged.
+ */
+
+#include <stdio.h>
+
+#define MAXLINE 1000 /* maximum input line size */
+
+unsigned getbits(unsigned x, int p, int n);
+unsigned setbits(unsigned x, int p, int n, unsigned y);
+unsigned invert(unsigned x, int p, int n);
+
+int main() {
+
+ printf("Type input line x n p expected\n");
+ printf(" %%x %%d %%d %%x\n");
+ unsigned x = 0;
+ int n = 0;
+ int p = 0;
+ unsigned result = 0;
+ unsigned expect = 0;
+
+ while(scanf("%x %d %d %x\n", &x, &n, &p, &expect) == 4) {
+ result = invert(x, n, p);
+ printf("result = 0x%x, expect = 0x%x\n", result, expect);
+ }
+ return 0;
+}
+
+/* getbits: get n bits from position p
+ *
+ * From K&R Cv2:
+ * getbits(x,p,n) returns the (right adjusted) n-bit field of x that begins at
+ * position p. We assume that bit position 0 is at the right end and that n
+ * and p are sensible positive values. For example, getbits(x,4,3) returns the
+ * three bits in bit positions 4, 3, and 2, right adjusted
+*/
+unsigned getbits(unsigned x, int p, int n) {
+ return (x >> (p+1-n)) & ~(~0 << n);
+}
+
+/* setbits: set n bits beginning at position p in x to rightmost n bits of y */
+unsigned setbits(unsigned x, int p, int n, unsigned y) {
+ return (x & ~(~(~0<<n) << (p-n+1))) | ((y & ~(~0<<n)) << (p-n+1));
+}
+
+/* invert: return x with n bits at position p inverted */
+unsigned invert(unsigned x, int p, int n) {
+ return x ^ (~(~0<<n) << (p-n+1));
+}
+
+/*
+ * 0x7de65afe 15 4 0x7de6aafe
+ * 0x7de65afe 0111 1101 1110 0110 0101 1010 1111 1110
+ * invert(x, 15, 4, y)
+ * 0x7de6aafe 0111 1101 1110 0110 1010 1010 1111 1110
+ *
+ * 0xadd230f1 23 6 0xad2e30f1
+ * 0xadd230f1 1010 1101 1101 0010 0011 0000 1111 0001
+ * invert(x, 23, 6, y)
+ * 0xad2e30f1 1010 1101 0010 1110 0011 0000 1111 0001
+ *
+ * 0x0feb3112 31 9 0xf06b3112
+ * 0x0feb3112 0000 1111 1110 1011 0011 0001 0001 0010
+ * invert(x, 31, 9, y)
+ * 0xf06b3112 1111 0000 0110 1011 0011 0001 0001 0010
+ *
+ * 0xa0b0c118 2 2 0xa0b0c11e
+ * 0xa0b0c118 1010 0000 1011 0000 1100 0001 0001 1000
+ * invert(x, 2, 2, y)
+ * 0xa0b0c11e 1010 0000 1011 0000 1100 0001 0001 1110
+ *
+ * 0x001992ba 17 8 0x001a6eba
+ * 0x001992ba 0000 0000 0001 1001 1001 0010 1011 1010
+ * invert(x, 17, 8, y)
+ * 0x001a6eba 0000 0000 0001 1010 0110 1110 1011 1010
+ *
+ * The remainder come from my old KNR test cases
+ */
