chore: fix some typos in comments (#429)

Signed-off-by: oftenoccur <[email protected]>

src/cost_model.rs

@@ -3,14 +3,14 @@ use crate::{
     Instruction,
 };
 
-// Returns the spent cycles to execute the secific instruction.
+// Returns the spent cycles to execute the specific instruction.
 // This function is usually used to write test cases, which can visually
 // display how many instructions are executed.
 pub fn constant_cycles(_: Instruction) -> u64 {
     1
 }
 
-// Returns the spent cycles to execute the secific instruction.
+// Returns the spent cycles to execute the specific instruction.
 // These values come from estimates of hardware execution speed.
 pub fn estimate_cycles(i: Instruction) -> u64 {
     match extract_opcode(i) {

src/machine/asm/mod.rs

@@ -128,7 +128,7 @@ fn check_memory_writable(
     check_memory(machine, page);
     machine.set_flag(page, FLAG_DIRTY)?;
 
-    // check next page if neccessary
+    // check next page if necessary
     let page_offset = addr as usize % RISCV_PAGESIZE;
     if page_offset + size > RISCV_PAGESIZE {
         let page = page + 1;
@@ -161,7 +161,7 @@ fn check_memory_executable(
     check_permission(machine, page, FLAG_EXECUTABLE)?;
     check_memory(machine, page);
 
-    // check next page if neccessary
+    // check next page if necessary
     let page_offset = addr as usize % RISCV_PAGESIZE;
     if page_offset + size > RISCV_PAGESIZE {
         let page = page + 1;
@@ -191,7 +191,7 @@ fn check_memory_inited(
     }
     check_memory(machine, page);
 
-    // check next page if neccessary
+    // check next page if necessary
     let page_offset = addr as usize % RISCV_PAGESIZE;
     if page_offset + size > RISCV_PAGESIZE {
         let page = page + 1;