[251] EDMUNDS, Justice.
In this case we determine whether petitioner Alford Jones is entitled to habeas corpus relief from incarceration on the grounds that he has accumulated various credits against his sentence. Because we conclude that he is lawfully incarcerated, we reverse the decision of the superior court.
The record indicates that Jones was charged with the 6 January 1975 murder of William B. Turner, Sr. Jones was convicted on 19 March 1975 in Superior Court, Lenoir County, and sentenced to death. In an opinion dated 17 June 1976, this Court found no error in Jones’s conviction and sentence. State v. Jones, 290 N.C. 292, 225 S.E.2d 549 (1976). On 1 September 1976, this Court entered an order vacating Jones’s sentence of death, pursuant to the opinion of the Supreme Court of the United States in Woodson v. North Carolina, 428 U.S. 280, 49 L. Ed. 2d 944 (1976). Upon remand to the superior court, Jones was sentenced to a term of life imprisonment on 27 September 1976. As of 30 November 2009, Jones had accrued good time totaling 14,041 days, gain time totaling 2,146 days, and merit time totaling 1,745 days.
On 18 November 2009, Jones filed a petition for writ of habeas corpus in Superior Court, Wayne County. Jones’s contention is that, when his good time, gain time, and merit time are credited to his life sentence, which is statutorily defined as a sentence of eighty years, he is entitled to unconditional release. After careful consideration, and relying on the opinion of the Court of Appeals in State v. Bowden, 193 N.C. App. 597, 668 S.E.2d 107 (2008), disc. rev. improvidently allowed, 363 N.C. 621, 683 S.E.2d 208 (2009), the superior court concluded that Jones was entitled to be awarded good time, gain time, and merit time by the Department of Correction (DOC) for all purposes, including calculation of Jones’s date of unconditional release; that Jones had served the entirety of the sentence imposed in his case; and that Jones was entitled to relief. Accordingly, the trial court allowed Jones’s petition for habeas corpus and ordered that Jones be released. This Court allowed DOC’s motion for temporary stay and granted its petition for writ of certiorari.1
“Every person restrained of his liberty is entitled to a remedy to inquire into the lawfulness thereof, and to remove the restraint, if [252] unlawful . . . .” N.C. Const, art. I, § 21 (codified at N.C.G.S. § 17-1 (2009)). Before this court, Jones again contends that he is unlawfully imprisoned because the life sentence imposed on him for first-degree murder committed in 1975 was defined as a term of eighty years and he has earned sufficient credits to have completed the sentence. Accordingly, Jones argues that he is entitled to immediate unconditional release. However, the record discloses that DOC allowed credits to Jones’s sentence only for limited purposes that did not include calculating an unconditional release date. We conclude that the limitations imposed by DOC on those credits are statutorily and constitutionally permissible. Therefore, his detention is lawful.
Jones is one of a group of prisoners, each of whom committed first-degree murder between 8 April 1974 and 30 June 1978 and were sentenced to life imprisonment, and it is this limited group that we consider in this opinion. At the time of petitioner’s offense, the controlling statute provided that “[a] sentence of life imprisonment shall be considered as a sentence of imprisonment for a term of 80 years in the State’s prison.” N.C.G.S. § 14-2 (Cum. Supp. 1974). Although DOC interpreted a life sentence imposed under that statute to be an indeterminate sentence that would expire only upon an inmate’s death, this statute unambiguously defined Jones’s sentence as a determinate term of imprisonment for eighty years. See Diaz v. Div. of Soc. Servs., 360 N.C. 384, 387, 628 S.E.2d 1, 3 (2006) (“When the language of a statute is clear and without ambiguity, it is the duty of this Court to give effect to the plain meaning of the statute, and judicial construction of legislative intent is not required.”).
However, while section 14-2 sets the term of imprisonment, that statute is silent as to the administration of the sentence. Instead, the General Assembly delegated that responsibility to DOC. N.C.G.S. § 148-11 (Cum. Supp. 1974) (“The Secretary [of Correction] shall propose rules and regulations for the government of the State prison system, which shall become effective when approved by the Department of Correction.”). The statutes further provide that “[t]he Secretary of Correction shall have control and custody of all prisoners serving sentence in the State prison system, and such prisoners shall be subject to all the rules and regulations legally adopted for the government thereof.” Id. § 148-4 (Cum. Supp. 1974). Specifically, “[t]he rules and regulations for the government of the State prison system may contain provisions relating to grades of prisoners, rewards and privileges applicable to the several classifications of prisoners as an inducement to good conduct, allowances of time for good behavior, [253] the amount of cash, clothing, etc., to be awarded prisoners after their discharge or parole.” Id. § 148-13 (1974).
Therefore, we must next consider the legality of the pertinent DOC regulations as they apply to petitioner. DOC is an arm of the executive branch of government. Id. § 143B-262(a) (2009). Under the doctrine of separation of powers, this Court has long held that when an agency of another branch of government is authorized to exercise regulatory power over the administration of prison sentences, we will defer to that authority to the extent the delegation is constitutional. See Jernigan v. State, 279 N.C. 556, 563, 184 S.E.2d 259, 265 (1971) (“This State is firmly committed to the doctrine that ‘[t]he legislative, executive, and supreme judicial powers of the State Government shall be forever separate and distinct from each other.’ ” (quoting N.C. Const, art. I, § 6 (1970) (alteration in original))).
“The functions of the court in regard to the punishment of crimes are to determine the guilt or innocence of the accused, and, if that determination be one of guilt, then to pronounce the punishment or penalty prescribed by law. The execution of the sentence belongs to a different department of the government. The manner of executing the sentence and the mitigation of punishment are determined by the legislative department, and what the Legislature has determined in that regard must be put in force and effect by administrative officers.”
Id. at 563-64, 184 S.E.2d at 265 (quoting People v. Joyce, 246 Ill. 124, 135, 92 N.E. 607, 612 (1910)); see also Bacon v. Lee, 353 N.C. 696, 716, 549 S.E.2d 840, 853-54, cert. denied, 533 U.S. 975, 150 L. Ed. 2d 804 (2001). “The punishment imposed in a particular case, if within statutory limits, is within the sound discretion of the presiding judge. The prison rules and regulations respecting rewards and privileges for good conduct (‘good time’) are strictly administrative and not judicial.” State v. Garris, 265 N.C. 711, 712, 144 S.E.2d 901, 902 (1965) (per curiam) (citing N.C.G.S. § 148-13); see also Goble v. Bounds, 281 N.C. 307, 312, 188 S.E.2d 347, 350 (1972) (holding that a prisoner’s complaint was appropriately dismissed by the superior court because questions whether the prisoner was entitled to parole, work release, or honor grade status “involve[] policy decisions which should be decided by the Department of Correction and the Board of Paroles,” not the courts). Accordingly, as a general rule, the judiciary will not review the DOC’s grant, forfeiture, or application of credits against a prisoner’s sentence.
[254] Nevertheless, DOC does not have carte blanche. “Of course, the responsibility for determining the limits of statutory grants of authority to an administrative agency is a judicial function for the courts to perform.” In re Appeal of Broad & Gales Creek Cmty. Ass’n, 300 N.C. 267, 280, 266 S.E.2d 645, 654 (1980). Further, “[w]hen a government action is challenged as unconstitutional, the courts have a duty to determine whether that action exceeds constitutional limits.” Leandro v. State, 346 N.C. 336, 345, 488 S.E.2d 249, 253 (1997).
The regulations promulgated by DOC have changed several times since Jones’s incarceration. Essentially, DOC’s regulations provide for good time, gain time, and merit time to be credited against an inmate’s sentence. See, e.g., Div. of Prisons, N.C. Dep’t of Corr., Policy and Procedure, ch. B, §§ .0109-.0116 (Oct. 5, 2007) (hereinafter DOC Manual); 5 NCAC 2B .0101-.0103 (Feb. 1976, Mar. 1980, Sept. 1983). Gain time and merit time are awarded to prisoners who perform work or otherwise take some action to qualify, while good time is automatically awarded to every prisoner. See, e.g., 5 NCAC 2B .0102-.0104. (Sept. 1983). Pursuant to the regulations, good time is subject to forfeiture, but only for reasons specified therein, such as major infractions, while gain time and merit time are not subject to forfeiture for misconduct. See, e.g., id. However, the distinctions between good time, gain time, and merit time, while of obvious importance to DOC and to inmates, are not material for our analysis as long as these credits are administered in a manner that satisfies statutory and constitutional requirements.
DOC argues, and the trial court found as fact, that “[t]he Department of Correction has never used good time, gain time, or merit time credits in the calculation of unconditional release dates for inmates who received sentences of life imprisonment.” More specifically, DOC acknowledges that Jones earned gain and merit time, but states that these credits were not applied to reduce the time to be served on his sentence in any way. Accordingly, the inmate records maintained for Jones by DOC show his sentence as “99/99/99,” a code that denotes a sentence of life imprisonment. These records also reflect a release date of “Life.” DOC’s position is that gain and merit time were only recorded in case Jones’s sentence was commuted by a governor, at which time they would be applied to calculate a release date. DOC further contends that it awarded Jones good time solely for the purposes of allowing him to move to the least restrictive custody grade and to calculate his parole eligibility date, and not for the purpose of allowing Jones unconditional release. Thus, according to DOC, vari[255] ous types of credits were awarded to Jones for different and limited purposes only, but no time was awarded for calculating a date of unconditional release. Because we defer to DOC’s inteipretation of its regulations, we need only consider whether DOC’s interpretation that Jones’s good time, gain time, and merit time credits were not awarded to him for purposes of unconditional release is statutorily and constitutionally permissible.
In making this determination, we first consider whether DOC’s administration of good time, gain time, and merit time credits is within the statutory authority delegated it by the General Assembly. An “agency has those powers that are explicitly granted in the statute plus those powers that are ascertainable as inherent in the underlying policies of the statute, and that may be fairly implied from the statute.” In re Appeal of Cmty. Ass’n, 300 N.C. at 280, 266 S.E.2d at 654-55 (citations omitted). At the time petitioner was sentenced, N.C.G.S. § 148-13 provided: “The rules and regulations for the government of the State prison system may contain provisions relating to grades of prisoners, rewards and privileges applicable to the several classifications of prisoners as an inducement to good conduct, allowances of time for good behavior....” N.C.G.S. § 148-13 (1974).2 In addition, at all relevant times N.C.G.S. § 143B-261 required DOC “to provide the necessary custody, supervision, and treatment to control and rehabilitate criminal offenders.” Id. §§ 143B-261 (2009), 143B-261 (Cum. Supp. 1974).
Under the rationale of In re Appeal of Cmty. Ass’n, 300 N.C. at 280, 266 S.E.2d at 654-55, implicit in DOC’s power to allow time for good behavior under section 148-13 is authority to determine the purposes for which that time is allowed. An award of time by DOC need not be an all-or-nothing award for unlimited uses. Discretion to determine the purposes for which time is awarded is consistent with such DOC goals as assuring that only those who can safely return to society are paroled or released and that they have been suitably prepared for outside life. See N.C.G.S. §§ 143B-261, 143B-262(a), 148-22 (2009). DOC’s application of its own regulations to accomplish these ends is “strictly administrative” and outside the purview of the courts. See [256] Garris, 265 N.C. at 712, 144 S.E.2d at 902. Accordingly, we conclude that DOC has acted within its statutory authority.
We now turn to the question whether DOC’s interpretation and implementation of its regulations are constitutional. Jones contends that DOC has violated his rights to due process and to equal protection. In addition, he argues that he has suffered an ex post facto violation. We address each of these claims.
The United States Supreme Court has held that “[l]iberty interests protected by the Fourteenth Amendment may arise from two sources — the Due Process Clause itself and the laws of the States.” Hewitt v. Helms, 459 U.S. 460, 466, 74 L. Ed. 2d 675, 685 (1983), abrogated in part on other grounds by Sandin v. Conner, 515 U.S. 472, 132 L. Ed. 2d 418 (1995). However, “due process is flexible and calls for such procedural protections as the particular situation demands. . . . [N]ot all situations calling for procedural safeguards call for the same kind of procedure.” Morrissey v. Brewer, 408 U.S. 471, 481, 33 L. Ed. 2d 484, 494 (1972). While a prisoner retains basic constitutional rights, State v. Primes, 314 N.C. 202, 208, 333 S.E.2d 278, 281 (1985), the Supreme Court has found that an inmate’s liberty interests derived from the Fourteenth Amendment are limited, given the nature of incarceration, Helms, 459 U.S. at 467, 74 L. Ed. 2d at 685 (“[0]ur decisions have consistently refused to recognize more than the most basic liberty interests in prisoners.”). Nevertheless, “a State may create a liberty interest protected by the Due Process Clause through its enactment of certain statutory or regulatory measures.” Id. at 469, 74 L. Ed. 2d at 686; see also Sandin v. Conner, 515 U.S. at 483-84, 132 L. Ed. 2d at 429. Prisoner benefits in the form of good time, gain time, and merit time arise from such statutes or regulations. See Wolff v. McDonnell, 418 U.S. 539, 557, 41 L. Ed. 2d 935, 951 (1974) (stating that “the Constitution itself does not guarantee good time credit for satisfactory behavior while in prison... [b]ut the State having created the right to good time and itself recognizing that its deprivation is a sanction authorized for major misconduct, the prisoner’s interest has real substance and is sufficiently embraced within Fourteenth Amendment ‘liberty’ to entitle him to those minimum procedures appropriate under the circumstances”).
The liberty interest alleged to be at issue here thus is one created by the State through its regulations. When a liberty interest is created by a State, it follows that the State can, within reasonable and constitutional limits, control the contours of the liberty interest it creates. In other words, the liberty interest created by the State through [257] its regulations may be limited to those particular aspects of an inmate’s incarceration that fall within the purview of those regulations. DOC has interpreted its regulations as permitting the award of different types of time credits for certain purposes and has, in fact, awarded those credits to Jones for those purposes. On the record before this Court, DOC has taken no action against Jones for punitive reasons. Because Jones has received the awards to which he is entitled for the purposes for which he is entitled, he has not been denied credits in which he has a constitutionally protected liberty interest.
Petitioner contends, however, that his credits should be applied toward calculation of the date of his unconditional release, We disagree. As indicated by Wolff, Helms, and Sandin, Jones’s liberty interest in good time, gain time, and merit time is limited. Thus, his liberty interest, if any, in having these credits used for the purpose of calculating his date of unconditional release is de minimis, particularly when contrasted with the State’s compelling interest in keeping inmates incarcerated until they can be released with safety to themselves and to the public. The record indicates that Jones is eligible for parole and has received annual parole reviews, but that the Parole Commission consistently has declined to parole him. Accordingly, Jones has received the process that is due him as an inmate eligible for parole, when the State’s corresponding interest is assuring that inmates are safely released under supervision. Assuming without deciding that DOC’s procedures for determining parole adequately protect an inmate’s due process rights to consideration for parole, those procedures are also adequate to preserve Jones’s constitutional rights while still ■ permitting the State to withhold application of Jones’s good time, gain time, and merit time to the calculation of a date for his unconditional release. He has no State-created right to have his time credits used to calculate his eligibility for unconditional release. Jones’s due process rights have not been violated.
This State interest in ensuring public safety is particularly pronounced when dealing with those convicted of first-degree murder. See State v. Rome, 348 N.C. 266, 271, 500 S.E.2d 77, 80 (1998) (describing first-degree murder as “this most serious crime”), superseded by statute, Act of May 8, 2001, ch. 81, secs. 1, 3, 2001 N.C. Sess. Laws 163, 163-65, on other grounds as recognized in State v. Defoe, 364 N.C. 29, 691 S.E.2d 1 (2010); see also Graham v. Florida, — U.S. —, —, 176 L. Ed. 2d 825, 842 (2010) (stating that “defendants who do not kill, intend to kill, or foresee that life will be taken are categorically less deserving of the most serious forms of punish[258] ment than are murderers”); State v. Davis, 290 N.C. 511, 548, 227 S.E.2d 97, 119-20 (1976) (“Murder in the first degree is obviously the most serious of the felonious homicides.”). The State has a duty to seek to ensure public safety through the orderly release of prisoners who are both under adequate supervision and prepared for resuming life outside of confinement. See N.C.G.S. § 15A-1371(d) (2009) (setting forth conditions under which the Post-Release Supervision and Parole Commission may refuse to release a prisoner on parole). DOC’s determination that Jones’s immediate unconditional release would endanger public safety in any respect is a compelling State interest outweighing any limited due process liberty interest Jones may have in application of his good time, gain time, and merit time credits to his unconditional release.
In addressing Jones’s contentions, we are aware that DOC’s regulations currently define good time, gain time, and merit time as “[t]ime credits applied to an inmate’s sentence that reduce[] the amount of time to be served” and state that “[g]ood time is sentence reduction credit awarded, at the rate of one day deducted for each day served in custody for good behavior and/or without an infraction of inmate conduct rules.” DOC Manual ch. B, § .0110(a), (f) (Oct. 5, 2007). These regulations were promulgated by DOC years after Jones was sentenced, see 5 NCAC 2B .0110(6) (Apr. 1995); id. 2B .0102 (Sept. 1983), when no challenge had been raised to the State’s position that those sentenced to life pursuant to the version of section 14-2 in effect between 8 April 1974 and 30 June 1978 had been given an indeterminate sentence. Except for this limited time period, life sentences unquestionably were and still are indeterminate sentences. No regulation explicitly provides that credits are to be used to calculate an unconditional release date, and DOC asserts that it never considered that these regulations applied to Jones or other inmates similarly situated for the purpose of calculating an unconditional release date. Because the regulations were understood to be inapplicable for that purpose, the State did not fully prepare Jones for unconditional release. In light of the compelling State interest in maintaining public safety, we conclude that these regulations do not require that DOC apply time credits for purposes of unconditional release to those who committed first-degree murder during the 8 April 1974 through 30 June 1978 time frame and were sentenced to life imprisonment.
We next consider Jones’s ex post facto argument. He contends that DOC’s interpretation of its regulations has retroactively increased the punishment for his offense after the offense was com[259] mitted. The trial court concluded that failing to use good time, gain time, and merit time credits to calculate an unconditional release date for Jones was not an ex post facto violation.
The constitutions of both the United States and North Carolina prohibit the enactment of ex post facto laws. U.S. Const, art. I, § 10, cl. 1 (“No state shall. . . pass any ... ex post facto law . . . .”); N.C. Const, art. I, § 16 (“Retrospective laws, punishing acts committed before the existence of such laws and by them only declared criminal, are oppressive, unjust, and incompatible with liberty, and therefore no ex post facto law shall be enacted.”). The federal and North Carolina constitutional ex post facto provisions are analyzed “under the same definition.” State v. Wiley, 355 N.C. 592, 625, 565 S.E.2d 22, 45 (2002), cert. denied, 537 U.S. 1117, 154 L. Ed. 2d 795 (2003). Most' pertinently here, the ex post facto prohibition applies to: “ ‘Every law that changes the punishment, and inflicts a greater punishment, than the law annexed to the crime, when committed.’ ” Id. (quoting Collins v. Youngblood, 497 U.S. 37, 42, 111 L. Ed. 2d 30, 38-39 (1990) (quoting Calder v. Bull, 3 U.S. 386, 390, 1 L. Ed. 648, 650 (1798))).
Legislation that retroactively alters sentence reduction credits in effect at the time a crime was committed can be an unconstitutional ex post facto law. See Weaver v. Graham, 450 U.S. 24, 25, 36, 67 L. Ed. 2d 17, 20-21, 28 (1981) (finding an ex post facto violation in Florida legislation that altered the availability of good time sentence reduction from a convicted prisoner’s sentence). However, Jones does not allege that any legislation or regulation has altered the award of sentence reduction credits. Nor has DOC changed its interpretation of its applicable regulations. Accordingly, the superior court correctly found that Jones has suffered no ex post facto violation.
Finally, Jones argues that DOC’s denial of good time, gain time, and merit time for the purpose of calculating an unconditional release date violates his right to equal protection of the law. Jones contends that his equal protection right prohibits the State from treating inmates who committed first-degree murder between 8 April 1974 and 30 June 1978 and were sentenced to life imprisonment under N.C.G.S. § 14-2, who are thus serving determinate sentences, differently from other inmates serving determinate sentences. “When a governmental classification does not burden the exercise of a fundamental right or operate to the peculiar disadvantage of a suspect class, the lower tier of equal protection analy[260] sis requiring that the classification be made upon a rational basis must be applied.” White v. Pate, 308 N.C. 759, 766, 304 S.E.2d 199, 204 (1983); see also Heller v. Doe ex rel. Doe, 509 U.S. 312, 319, 125 L. Ed. 2d 257, 270 (1993). Thus, “equal protection of the laws is not denied by a statute prescribing the punishment to be inflicted on a person convicted of crime unless it prescribes different punishment for the same acts committed under the same circumstances by persons in like situation.” State v. Benton, 276 N.C. 641, 660, 174 S.E.2d 793, 805 (1970), quoted in State v. Dunlap, 298 N.C. 725, 735-36, 259 S.E.2d 893, 899 (1979).
Jones was convicted of a different crime than others serving determinate sentences under statutes other than N.C.G.S. § 14-2, even if the sentences of some of those others are for eighty years or even longer (perhaps due to the imposition of consecutive sentences). The fact that Jones is serving a sentence for first-degree murder reasonably suggests that he presents a greater threat to society than prisoners convicted of other offenses. Thus, DOC has a rational basis for denying petitioner good time, gain time, and merit time for the purposes of unconditional release, even though these same credits have been awarded for that purpose to other prisoners with determinate sentences.
Accordingly, we hold that Jones is legally incarcerated. The holding of the trial court to the contrary is reversed.
REVERSED.